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introduces functional / factory & forward
[SVN r49957]
This commit is contained in:
Tobias Schwinger
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factory/doc/Jamfile
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factory/doc/Jamfile
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# (C) Copyright Tobias Schwinger
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#
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# Use modification and distribution are subject to the boost Software License,
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# Version 1.0. (See http:/\/www.boost.org/LICENSE_1_0.txt).
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using quickbook ;
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xml factory : factory.qbk ;
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boostbook standalone : factory
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:
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<xsl:param>boost.root=../../../../..
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<xsl:param>boost.libraries=../../../../libraries.htm
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<xsl:param>chunk.section.depth=0
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<xsl:param>chunk.first.sections=0
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<xsl:param>generate.section.toc.level=2
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<xsl:param>toc.max.depth=1
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;
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384
factory/doc/factory.qbk
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factory/doc/factory.qbk
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[library Boost.Functional/Factory
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[quickbook 1.3]
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[version 1.0]
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[authors [Schwinger, Tobias]]
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[copyright 2007 2008 Tobias Schwinger]
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[license
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Distributed under the Boost Software License, Version 1.0.
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(See accompanying file LICENSE_1_0.txt or copy at
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[@http://www.boost.org/LICENSE_1_0.txt])
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]
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[purpose Function object templates for object creation.]
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[category higher-order]
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[category generic]
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[last-revision $Date: 2008/11/01 21:44:52 $]
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]
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[def __boost_bind__ [@http://www.boost.org/libs/bind/bind.html Boost.Bind]]
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[def __boost__bind__ [@http://www.boost.org/libs/bind/bind.html `boost::bind`]]
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[def __boost__forward_adapter__ [@http://www.boost.org/libs/functional/forward/doc/index.html `boost::forward_adapter`]]
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[def __fusion_functional_adapters__ [@http://www.boost.org/libs/fusion/doc/html/functional.html Fusion Functional Adapters]]
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[def __boost_function__ [@http://www.boost.org/doc/html/function.html Boost.Function]]
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[def __boost__function__ [@http://www.boost.org/doc/html/function.html `boost::function`]]
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[def __smart_pointers__ [@http://www.boost.org/libs/smart_ptr/index.html Smart Pointers]]
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[def __boost__shared_ptr__ [@http://www.boost.org/libs/smart_ptr/shared_ptr.htm `boost::shared_ptr`]]
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[def __std__map__ [@http://www.sgi.com/tech/stl/map.html `std::map`]]
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[def __std__string__ [@http://www.sgi.com/tech/stl/string.html `std::string`]]
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[def __std_allocator__ [@http://www.sgi.com/tech/stl/concepts/allocator.html Allocator]]
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[def __std_allocators__ [@http://www.sgi.com/tech/stl/concepts/allocator.html Allocators]]
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[def __boost__ptr_map__ [@http://www.boost.org/libs/ptr_container/doc/ptr_map.html `__boost__ptr_map__`]]
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[def __boost__factory__ `boost::factory`]
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[def __boost__value_factory__ `boost::value_factory`]
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[def __factory__ `factory`]
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[def __value_factory__ `value_factory`]
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[section Brief Description]
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The template __boost__factory__ lets you encapsulate a `new` expression
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as a function object, __boost__value_factory__ encapsulates a constructor
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invocation without `new`.
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__boost__factory__<T*>()(arg1,arg2,arg3)
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// same as new T(arg1,arg2,arg3)
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__boost__value_factory__<T>()(arg1,arg2,arg3)
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// same as T(arg1,arg2,arg3)
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For technical reasons the arguments to the function objects have to be
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LValues. A factory that also accepts RValues can be composed using the
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__boost__forward_adapter__ or __boost__bind__.
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[endsect]
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[section Background]
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In traditional Object Oriented Programming a Factory is an object implementing
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an interface of one or more methods that construct objects conforming to known
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interfaces.
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// assuming a_concrete_class and another_concrete_class are derived
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// from an_abstract_class
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class a_factory
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{
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public:
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virtual an_abstract_class* create() const = 0;
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virtual ~a_factory() { }
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};
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class a_concrete_factory : public a_factory
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{
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public:
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virtual an_abstract_class* create() const
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{
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return new a_concrete_class();
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}
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};
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class another_concrete_factory : public a_factory
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{
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public:
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virtual an_abstract_class* create() const
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{
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return new another_concrete_class();
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}
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};
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// [...]
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int main()
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{
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__boost__ptr_map__<__std__string__,a_factory> factories;
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// [...]
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factories.insert("a_name",std::auto_ptr<a_factory>(
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new a_concrete_factory));
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factories.insert("another_name",std::auto_ptr<a_factory>(
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new another_concrete_factory));
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// [...]
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std::auto_ptr<an_abstract_factory> x = factories[some_name]->create();
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// [...]
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}
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This approach has several drawbacks. The most obvious one is that there is
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lots of boilerplate code. In other words there is too much code to express
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a rather simple intention. We could use templates to get rid of some of it
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but the approach remains inflexible:
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o We may want a factory that takes some arguments that are forwarded to
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the constructor,
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o we will probably want to use smart pointers,
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o we may want several member functions to create different kinds of
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objects,
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o we might not necessarily need a polymorphic base class for the objects,
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o as we will see, we do not need a factory base class at all,
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o we might want to just call the constructor - without `new` to create
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an object on the stack, and
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o finally we might want to use customized memory management.
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Experience has shown that using function objects and generic Boost components
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for their composition, Design Patterns that describe callback mechasisms
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(typically requiring a high percentage of boilerplate code with pure Object
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Oriented methodology) become implementable with just few code lines and without
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extra classes.
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Factories are callback mechanisms for constructors, so we provide two class
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templates, __boost__value_factory__ and __boost__factory__, that encasulate
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object construction via direct application of the constructor and the `new`
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operator, respectively.
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We let the function objects forward their arguments to the construction
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expressions they encapsulate. Overthis __boost__factory__ optionally allows
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the use of smart pointers and __std_allocators__.
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Compile-time polymorphism can be used where appropriate,
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template< class T >
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void do_something()
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{
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// [...]
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T x = T(a,b);
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// for conceptually similar objects x we neither need virtual
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// functions nor a common base class in this context.
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// [...]
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}
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Now, to allow inhomogenous signaturs for the constructors of the types passed
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in for `T` we can use __value_factory__ and __boost__bind__ to normalize between
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them.
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template< class ValueFactory >
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void do_something(ValueFactory make_obj = ValueFactory())
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{
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// [...]
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typename ValueFactory::result_type x = make_obj(a,b);
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// for conceptually similar objects x we neither need virtual
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// functions nor a common base class in this context.
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// [...]
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}
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int main()
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{
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// [...]
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do_something(__boost__value_factory__<X>());
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do_something(boost::bind(__boost__value_factory__<Y>(),_1,5,_2));
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// construct X(a,b) and Y(a,5,b), respectively.
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// [...]
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}
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Maybe we want our objects to outlive the function's scope, in this case we
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have to use dynamic allocation;
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template< class Factory >
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whatever do_something(Factory new_obj = Factory())
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{
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typename Factory::result_type ptr = new_obj(a,b);
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// again, no common base class or virtual functions needed,
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// we could enforce a polymorphic base by writing e.g.
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// boost::shared_ptr<base>
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// instead of
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// typename Factory::result_type
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// above.
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// Note that we are also free to have the type erasure happen
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// somewhere else (e.g. in the constructor of this function's
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// result type).
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// [...]
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}
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// [... call do_something like above but with __factory__ instead
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// of __value_factory__]
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Although we might have created polymorphic objects in the previous example,
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we have used compile time polymorphism for the factory. If we want to erase
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the type of the factory and thus allow polymorphism at run time, we can
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use __boost_function__ to do so. The first example can be rewritten as
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follows.
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typedef boost::function< an_abstract_class*() > a_factory;
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// [...]
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int main()
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{
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__std__map__<__std__string__,a_factory> factories;
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// [...]
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factories["a_name"] = __boost__factory__<a_concrete_class*>();
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factories["another_name"] =
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__boost__factory__<another_concrete_class*>();
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// [...]
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}
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Of course we can just as easy create factories that take arguments and/or
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return __smart_pointers__.
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[endsect]
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[section:reference Reference]
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[section value_factory]
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[heading Description]
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Function object template that invokes the constructor of the type `T`.
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[heading Header]
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#include <boost/functional/value_factory.hpp>
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[heading Synopsis]
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namespace boost
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{
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template< typename T >
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class value_factory;
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}
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[variablelist Notation
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[[`T`] [an arbitrary type with at least one public constructor]]
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[[`a0`...`aN`] [argument LValues to a constructor of `T`]]
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[[`F`] [the type `value_factory<F>`]]
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[[`f`] [an instance object of `F`]]
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]
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[heading Expression Semantics]
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[table
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[[Expression] [Semantics]]
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[[`F()`] [creates an object of type `F`.]]
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[[`F(f)`] [creates an object of type `F`.]]
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[[`f(a0`...`aN)`] [returns `T(a0`...`aN)`.]]
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[[`F::result_type`] [is the type `T`.]]
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]
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[heading Limits]
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The macro BOOST_FUNCTIONAL_VALUE_FACTORY_MAX_ARITY can be defined to set the
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maximum arity. It defaults to 10.
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[endsect]
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[section factory]
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[heading Description]
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Function object template that dynamically constructs a pointee object for
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the type of pointer given as template argument. Smart pointers may be used
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for the template argument, given that `boost::pointee<Pointer>::type` yields
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the pointee type.
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If an __allocator__ is given, it is used for memory allocation and the
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placement form of the `new` operator is used to construct the object.
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A function object that calls the destructor and deallocates the memory
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with a copy of the Allocator is used for the second constructor argument
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of `Pointer` (thus it must be a __smart_pointer__ that provides a suitable
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constructor, such as __boost__shared_ptr__).
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If a third template argument is `factory_passes_alloc_to_smart_pointer`,
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the allocator itself is used for the third constructor argument of `Pointer`
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(__boost__shared_ptr__ then uses the allocator to manage the memory of its
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seperately allocated reference counter).
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[heading Header]
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#include <boost/functional/factory.hpp>
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[heading Synopsis]
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namespace boost
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{
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enum factory_alloc_propagation
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{
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factory_alloc_for_pointee_and_deleter,
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factory_passes_alloc_to_smart_pointer
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};
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template< typename Pointer,
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class Allocator = boost::none_t,
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factory_alloc_propagation AllocProp =
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factory_alloc_for_pointee_and_deleter >
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class factory;
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}
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[variablelist Notation
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[[`T`] [an arbitrary type with at least one public constructor]]
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[[`P`] [pointer or smart pointer to `T`]]
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[[`a0`...`aN`] [argument LValues to a constructor of `T`]]
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[[`F`] [the type `factory<P>`]]
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[[`f`] [an instance object of `F`]]
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]
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[heading Expression Semantics]
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[table
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[[Expression] [Semantics]]
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[[`F()`] [creates an object of type `F`.]]
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[[`F(f)`] [creates an object of type `F`.]]
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[[`f(a0`...`aN)`] [dynamically creates an object of type `T` using
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`a0`...`aN` as arguments for the constructor invocation.]]
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[[`F::result_type`] [is the type `P` with top-level cv-qualifiers removed.]]
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]
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[heading Limits]
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The macro BOOST_FUNCTIONAL_FACTORY_MAX_ARITY can be defined to set the
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maximum arity. It defaults to 10.
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[endsect]
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[endsect]
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[section Acknowledgements]
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Eric Niebler requested a function to invoke a type's constructor (with the
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arguments supplied as a Tuple) as a Fusion feature. These Factory utilities are
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a factored-out generalization of this idea.
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Dave Abrahams suggested Smart Pointer support for exception safety, providing
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useful hints for the implementation.
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Joel de Guzman's documentation style was copied from Fusion.
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Further, I want to thank Peter Dimov for sharing his insights on language
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details and their evolution.
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[endsect]
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[section References]
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||||
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||||
# [@http://en.wikipedia.org/wiki/Design_Patterns Design Patterns],
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Gamma et al. - Addison Wesley Publishing, 1995
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||||
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||||
# [@http://www.sgi.com/tech/stl/ Standard Template Library Programmer's Guide],
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Hewlett-Packard Company, 1994
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||||
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||||
# [@http://www.boost.org/libs/bind/bind.html Boost.Bind],
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||||
Peter Dimov, 2001-2005
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||||
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||||
# [@http://www.boost.org/doc/html/function.html Boost.Function],
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Douglas Gregor, 2001-2004
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||||
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||||
[endsect]
|
||||
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528
factory/doc/html/boostbook.css
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528
factory/doc/html/boostbook.css
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/*=============================================================================
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||||
Copyright (c) 2004 Joel de Guzman
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||||
http://spirit.sourceforge.net/
|
||||
|
||||
Use, modification and distribution is subject to the Boost Software
|
||||
License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
|
||||
http://www.boost.org/LICENSE_1_0.txt)
|
||||
=============================================================================*/
|
||||
|
||||
/*=============================================================================
|
||||
Body defaults
|
||||
=============================================================================*/
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||||
|
||||
body
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{
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margin: 1em;
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font-family: sans-serif;
|
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}
|
||||
|
||||
/*=============================================================================
|
||||
Paragraphs
|
||||
=============================================================================*/
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||||
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p
|
||||
{
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||||
text-align: left;
|
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font-size: 10pt;
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||||
line-height: 1.15;
|
||||
}
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|
||||
/*=============================================================================
|
||||
Program listings
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=============================================================================*/
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||||
|
||||
/* Code on paragraphs */
|
||||
p tt.computeroutput
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||||
{
|
||||
font-size: 9pt;
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}
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|
||||
pre.synopsis
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{
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font-size: 90%;
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margin: 1pc 4% 0pc 4%;
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padding: 0.5pc 0.5pc 0.5pc 0.5pc;
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}
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.programlisting,
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.screen
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{
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font-size: 9pt;
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display: block;
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margin: 1pc 4% 0pc 4%;
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padding: 0.5pc 0.5pc 0.5pc 0.5pc;
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}
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/* Program listings in tables don't get borders */
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td .programlisting,
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td .screen
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{
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margin: 0pc 0pc 0pc 0pc;
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padding: 0pc 0pc 0pc 0pc;
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}
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/*=============================================================================
|
||||
Headings
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||||
=============================================================================*/
|
||||
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h1, h2, h3, h4, h5, h6
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{
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text-align: left;
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margin: 1em 0em 0.5em 0em;
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font-weight: bold;
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}
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h1 { font: 140% }
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h2 { font: bold 140% }
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h3 { font: bold 130% }
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h4 { font: bold 120% }
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h5 { font: italic 110% }
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h6 { font: italic 100% }
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/* Top page titles */
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title,
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h1.title,
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h2.title
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h3.title,
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h4.title,
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h5.title,
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h6.title,
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.refentrytitle
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{
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font-weight: bold;
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margin-bottom: 1pc;
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}
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h1.title { font-size: 140% }
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h2.title { font-size: 140% }
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h3.title { font-size: 130% }
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h4.title { font-size: 120% }
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h5.title { font-size: 110% }
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h6.title { font-size: 100% }
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598
factory/doc/html/index.html
Normal file
598
factory/doc/html/index.html
Normal file
@@ -0,0 +1,598 @@
|
||||
<html>
|
||||
<head>
|
||||
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
|
||||
<title>Chapter<EFBFBD>1.<2E>Boost.Functional/Factory 1.0</title>
|
||||
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|
||||
<meta name="generator" content="DocBook XSL Stylesheets V1.68.1">
|
||||
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|
||||
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|
||||
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|
||||
<table cellpadding="2" width="100%"><tr>
|
||||
<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../boost.png"></td>
|
||||
<td align="center"><a href="../../../../../index.html">Home</a></td>
|
||||
<td align="center"><a href="../../../../libraries.htm">Libraries</a></td>
|
||||
<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
|
||||
<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
|
||||
<td align="center"><a href="../../../../../more/index.htm">More</a></td>
|
||||
</tr></table>
|
||||
<hr>
|
||||
<div class="spirit-nav"></div>
|
||||
<div class="chapter" lang="en">
|
||||
<div class="titlepage"><div>
|
||||
<div><h2 class="title">
|
||||
<a name="boost_functional_factory"></a>Chapter<EFBFBD>1.<2E>Boost.Functional/Factory 1.0</h2></div>
|
||||
<div><div class="author"><h3 class="author">
|
||||
<span class="firstname">Tobias</span> <span class="surname">Schwinger</span>
|
||||
</h3></div></div>
|
||||
<div><p class="copyright">Copyright <20> 2007, 2008 Tobias Schwinger</p></div>
|
||||
<div><div class="legalnotice">
|
||||
<a name="id934161"></a><p>
|
||||
Distributed under the Boost Software License, Version 1.0. (See accompanying
|
||||
file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
|
||||
</p>
|
||||
</div></div>
|
||||
</div></div>
|
||||
<div class="toc">
|
||||
<p><b>Table of Contents</b></p>
|
||||
<dl>
|
||||
<dt><span class="section"><a href="index.html#boost_functional_factory.brief_description">Brief Description</a></span></dt>
|
||||
<dt><span class="section"><a href="index.html#boost_functional_factory.background">Background</a></span></dt>
|
||||
<dt><span class="section"><a href="index.html#boost_functional_factory.reference"> Reference</a></span></dt>
|
||||
<dt><span class="section"><a href="index.html#boost_functional_factory.acknowledgements">Acknowledgements</a></span></dt>
|
||||
<dt><span class="section"><a href="index.html#boost_functional_factory.references">References</a></span></dt>
|
||||
</dl>
|
||||
</div>
|
||||
<div class="section" lang="en">
|
||||
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
|
||||
<a name="boost_functional_factory.brief_description"></a><a href="index.html#boost_functional_factory.brief_description" title="Brief Description">Brief Description</a></h2></div></div></div>
|
||||
<p>
|
||||
The template <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">factory</span></code> lets you encapsulate a <code class="computeroutput"><span class="keyword">new</span></code> expression as a function object, <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">value_factory</span></code>
|
||||
encapsulates a constructor invocation without <code class="computeroutput"><span class="keyword">new</span></code>.
|
||||
</p>
|
||||
<pre class="programlisting"><code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">factory</span></code><span class="special"><</span><span class="identifier">T</span><span class="special">*>()(</span><span class="identifier">arg1</span><span class="special">,</span><span class="identifier">arg2</span><span class="special">,</span><span class="identifier">arg3</span><span class="special">)</span>
|
||||
<span class="comment">// same as new T(arg1,arg2,arg3)
|
||||
</span>
|
||||
<code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">value_factory</span></code><span class="special"><</span><span class="identifier">T</span><span class="special">>()(</span><span class="identifier">arg1</span><span class="special">,</span><span class="identifier">arg2</span><span class="special">,</span><span class="identifier">arg3</span><span class="special">)</span>
|
||||
<span class="comment">// same as T(arg1,arg2,arg3)
|
||||
</span></pre>
|
||||
<p>
|
||||
For technical reasons the arguments to the function objects have to be LValues.
|
||||
A factory that also accepts RValues can be composed using the <a href="http://www.boost.org/libs/functional/forward/doc/index.html" target="_top"><code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">forward_adapter</span></code></a>
|
||||
or <a href="http://www.boost.org/libs/bind/bind.html" target="_top"><code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">bind</span></code></a>.
|
||||
</p>
|
||||
</div>
|
||||
<div class="section" lang="en">
|
||||
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
|
||||
<a name="boost_functional_factory.background"></a><a href="index.html#boost_functional_factory.background" title="Background">Background</a></h2></div></div></div>
|
||||
<p>
|
||||
In traditional Object Oriented Programming a Factory is an object implementing
|
||||
an interface of one or more methods that construct objects conforming to known
|
||||
interfaces.
|
||||
</p>
|
||||
<pre class="programlisting"><span class="comment">// assuming a_concrete_class and another_concrete_class are derived
|
||||
</span><span class="comment">// from an_abstract_class
|
||||
</span>
|
||||
<span class="keyword">class</span> <span class="identifier">a_factory</span>
|
||||
<span class="special">{</span>
|
||||
<span class="keyword">public</span><span class="special">:</span>
|
||||
<span class="keyword">virtual</span> <span class="identifier">an_abstract_class</span><span class="special">*</span> <span class="identifier">create</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span>
|
||||
<span class="keyword">virtual</span> <span class="special">~</span><span class="identifier">a_factory</span><span class="special">()</span> <span class="special">{</span> <span class="special">}</span>
|
||||
<span class="special">};</span>
|
||||
|
||||
<span class="keyword">class</span> <span class="identifier">a_concrete_factory</span> <span class="special">:</span> <span class="keyword">public</span> <span class="identifier">a_factory</span>
|
||||
<span class="special">{</span>
|
||||
<span class="keyword">public</span><span class="special">:</span>
|
||||
<span class="keyword">virtual</span> <span class="identifier">an_abstract_class</span><span class="special">*</span> <span class="identifier">create</span><span class="special">()</span> <span class="keyword">const</span>
|
||||
<span class="special">{</span>
|
||||
<span class="keyword">return</span> <span class="keyword">new</span> <span class="identifier">a_concrete_class</span><span class="special">();</span>
|
||||
<span class="special">}</span>
|
||||
<span class="special">};</span>
|
||||
|
||||
<span class="keyword">class</span> <span class="identifier">another_concrete_factory</span> <span class="special">:</span> <span class="keyword">public</span> <span class="identifier">a_factory</span>
|
||||
<span class="special">{</span>
|
||||
<span class="keyword">public</span><span class="special">:</span>
|
||||
<span class="keyword">virtual</span> <span class="identifier">an_abstract_class</span><span class="special">*</span> <span class="identifier">create</span><span class="special">()</span> <span class="keyword">const</span>
|
||||
<span class="special">{</span>
|
||||
<span class="keyword">return</span> <span class="keyword">new</span> <span class="identifier">another_concrete_class</span><span class="special">();</span>
|
||||
<span class="special">}</span>
|
||||
<span class="special">};</span>
|
||||
|
||||
<span class="comment">// [...]
|
||||
</span>
|
||||
<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span>
|
||||
<span class="special">{</span>
|
||||
<a href="http://www.boost.org/libs/ptr_container/doc/ptr_map.html" target="_top"><code class="computeroutput"><span class="identifier">__boost__ptr_map__</span></code></a><span class="special"><</span><a href="http://www.sgi.com/tech/stl/string.html" target="_top"><code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span></code></a><span class="special">,</span><span class="identifier">a_factory</span><span class="special">></span> <span class="identifier">factories</span><span class="special">;</span>
|
||||
|
||||
<span class="comment">// [...]
|
||||
</span>
|
||||
<span class="identifier">factories</span><span class="special">.</span><span class="identifier">insert</span><span class="special">(</span><span class="string">"a_name"</span><span class="special">,</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">auto_ptr</span><span class="special"><</span><span class="identifier">a_factory</span><span class="special">>(</span>
|
||||
<span class="keyword">new</span> <span class="identifier">a_concrete_factory</span><span class="special">));</span>
|
||||
<span class="identifier">factories</span><span class="special">.</span><span class="identifier">insert</span><span class="special">(</span><span class="string">"another_name"</span><span class="special">,</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">auto_ptr</span><span class="special"><</span><span class="identifier">a_factory</span><span class="special">>(</span>
|
||||
<span class="keyword">new</span> <span class="identifier">another_concrete_factory</span><span class="special">));</span>
|
||||
|
||||
<span class="comment">// [...]
|
||||
</span>
|
||||
<span class="identifier">std</span><span class="special">::</span><span class="identifier">auto_ptr</span><span class="special"><</span><span class="identifier">an_abstract_factory</span><span class="special">></span> <span class="identifier">x</span> <span class="special">=</span> <span class="identifier">factories</span><span class="special">[</span><span class="identifier">some_name</span><span class="special">]-></span><span class="identifier">create</span><span class="special">();</span>
|
||||
|
||||
<span class="comment">// [...]
|
||||
</span><span class="special">}</span>
|
||||
</pre>
|
||||
<p>
|
||||
This approach has several drawbacks. The most obvious one is that there is
|
||||
lots of boilerplate code. In other words there is too much code to express
|
||||
a rather simple intention. We could use templates to get rid of some of it
|
||||
but the approach remains inflexible:
|
||||
</p>
|
||||
<pre class="programlisting"><span class="identifier">o</span> <span class="identifier">We</span> <span class="identifier">may</span> <span class="identifier">want</span> <span class="identifier">a</span> <span class="identifier">factory</span> <span class="identifier">that</span> <span class="identifier">takes</span> <span class="identifier">some</span> <span class="identifier">arguments</span> <span class="identifier">that</span> <span class="identifier">are</span> <span class="identifier">forwarded</span> <span class="identifier">to</span>
|
||||
<span class="identifier">the</span> <span class="identifier">constructor</span><span class="special">,</span>
|
||||
<span class="identifier">o</span> <span class="identifier">we</span> <span class="identifier">will</span> <span class="identifier">probably</span> <span class="identifier">want</span> <span class="identifier">to</span> <span class="identifier">use</span> <span class="identifier">smart</span> <span class="identifier">pointers</span><span class="special">,</span>
|
||||
<span class="identifier">o</span> <span class="identifier">we</span> <span class="identifier">may</span> <span class="identifier">want</span> <span class="identifier">several</span> <span class="identifier">member</span> <span class="identifier">functions</span> <span class="identifier">to</span> <span class="identifier">create</span> <span class="identifier">different</span> <span class="identifier">kinds</span> <span class="identifier">of</span>
|
||||
<span class="identifier">objects</span><span class="special">,</span>
|
||||
<span class="identifier">o</span> <span class="identifier">we</span> <span class="identifier">might</span> <span class="keyword">not</span> <span class="identifier">necessarily</span> <span class="identifier">need</span> <span class="identifier">a</span> <span class="identifier">polymorphic</span> <span class="identifier">base</span> <span class="keyword">class</span> <span class="keyword">for</span> <span class="identifier">the</span> <span class="identifier">objects</span><span class="special">,</span>
|
||||
<span class="identifier">o</span> <span class="identifier">as</span> <span class="identifier">we</span> <span class="identifier">will</span> <span class="identifier">see</span><span class="special">,</span> <span class="identifier">we</span> <span class="keyword">do</span> <span class="keyword">not</span> <span class="identifier">need</span> <span class="identifier">a</span> <span class="identifier">factory</span> <span class="identifier">base</span> <span class="keyword">class</span> <span class="identifier">at</span> <span class="identifier">all</span><span class="special">,</span>
|
||||
<span class="identifier">o</span> <span class="identifier">we</span> <span class="identifier">might</span> <span class="identifier">want</span> <span class="identifier">to</span> <span class="identifier">just</span> <span class="identifier">call</span> <span class="identifier">the</span> <span class="identifier">constructor</span> <span class="special">-</span> <span class="identifier">without</span> #<span class="keyword">new</span># <span class="identifier">to</span> <span class="identifier">create</span>
|
||||
<span class="identifier">an</span> <span class="identifier">object</span> <span class="identifier">on</span> <span class="identifier">the</span> <span class="identifier">stack</span><span class="special">,</span> <span class="keyword">and</span>
|
||||
<span class="identifier">o</span> <span class="identifier">finally</span> <span class="identifier">we</span> <span class="identifier">might</span> <span class="identifier">want</span> <span class="identifier">to</span> <span class="identifier">use</span> <span class="identifier">customized</span> <span class="identifier">memory</span> <span class="identifier">management</span><span class="special">.</span>
|
||||
</pre>
|
||||
<p>
|
||||
Experience has shown that using function objects and generic Boost components
|
||||
for their composition, Design Patterns that describe callback mechasisms (typically
|
||||
requiring a high percentage of boilerplate code with pure Object Oriented methodology)
|
||||
become implementable with just few code lines and without extra classes.
|
||||
</p>
|
||||
<p>
|
||||
Factories are callback mechanisms for constructors, so we provide two class
|
||||
templates, <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">value_factory</span></code> and <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">factory</span></code>,
|
||||
that encasulate object construction via direct application of the constructor
|
||||
and the <code class="computeroutput"><span class="keyword">new</span></code> operator, respectively.
|
||||
</p>
|
||||
<p>
|
||||
We let the function objects forward their arguments to the construction expressions
|
||||
they encapsulate. Overthis <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">factory</span></code>
|
||||
optionally allows the use of smart pointers and <a href="http://www.sgi.com/tech/stl/concepts/allocator.html" target="_top">Allocators</a>.
|
||||
</p>
|
||||
<p>
|
||||
Compile-time polymorphism can be used where appropriate,
|
||||
</p>
|
||||
<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span> <span class="keyword">class</span> <span class="identifier">T</span> <span class="special">></span>
|
||||
<span class="keyword">void</span> <span class="identifier">do_something</span><span class="special">()</span>
|
||||
<span class="special">{</span>
|
||||
<span class="comment">// [...]
|
||||
</span> <span class="identifier">T</span> <span class="identifier">x</span> <span class="special">=</span> <span class="identifier">T</span><span class="special">(</span><span class="identifier">a</span><span class="special">,</span><span class="identifier">b</span><span class="special">);</span>
|
||||
|
||||
<span class="comment">// for conceptually similar objects x we neither need virtual
|
||||
</span> <span class="comment">// functions nor a common base class in this context.
|
||||
</span> <span class="comment">// [...]
|
||||
</span><span class="special">}</span>
|
||||
</pre>
|
||||
<p>
|
||||
Now, to allow inhomogenous signaturs for the constructors of the types passed
|
||||
in for <code class="computeroutput"><span class="identifier">T</span></code> we can use <code class="computeroutput"><span class="identifier">value_factory</span></code> and <a href="http://www.boost.org/libs/bind/bind.html" target="_top"><code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">bind</span></code></a>
|
||||
to normalize between them.
|
||||
</p>
|
||||
<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span> <span class="keyword">class</span> <span class="identifier">ValueFactory</span> <span class="special">></span>
|
||||
<span class="keyword">void</span> <span class="identifier">do_something</span><span class="special">(</span><span class="identifier">ValueFactory</span> <span class="identifier">make_obj</span> <span class="special">=</span> <span class="identifier">ValueFactory</span><span class="special">())</span>
|
||||
<span class="special">{</span>
|
||||
<span class="comment">// [...]
|
||||
</span> <span class="keyword">typename</span> <span class="identifier">ValueFactory</span><span class="special">::</span><span class="identifier">result_type</span> <span class="identifier">x</span> <span class="special">=</span> <span class="identifier">make_obj</span><span class="special">(</span><span class="identifier">a</span><span class="special">,</span><span class="identifier">b</span><span class="special">);</span>
|
||||
|
||||
<span class="comment">// for conceptually similar objects x we neither need virtual
|
||||
</span> <span class="comment">// functions nor a common base class in this context.
|
||||
</span> <span class="comment">// [...]
|
||||
</span><span class="special">}</span>
|
||||
|
||||
<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span>
|
||||
<span class="special">{</span>
|
||||
<span class="comment">// [...]
|
||||
</span>
|
||||
<span class="identifier">do_something</span><span class="special">(</span><code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">value_factory</span></code><span class="special"><</span><span class="identifier">X</span><span class="special">>());</span>
|
||||
<span class="identifier">do_something</span><span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">bind</span><span class="special">(</span><code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">value_factory</span></code><span class="special"><</span><span class="identifier">Y</span><span class="special">>(),</span><span class="identifier">_1</span><span class="special">,</span><span class="number">5</span><span class="special">,</span><span class="identifier">_2</span><span class="special">));</span>
|
||||
<span class="comment">// construct X(a,b) and Y(a,5,b), respectively.
|
||||
</span>
|
||||
<span class="comment">// [...]
|
||||
</span><span class="special">}</span>
|
||||
</pre>
|
||||
<p>
|
||||
Maybe we want our objects to outlive the function's scope, in this case we
|
||||
have to use dynamic allocation;
|
||||
</p>
|
||||
<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span> <span class="keyword">class</span> <span class="identifier">Factory</span> <span class="special">></span>
|
||||
<span class="identifier">whatever</span> <span class="identifier">do_something</span><span class="special">(</span><span class="identifier">Factory</span> <span class="identifier">new_obj</span> <span class="special">=</span> <span class="identifier">Factory</span><span class="special">())</span>
|
||||
<span class="special">{</span>
|
||||
<span class="keyword">typename</span> <span class="identifier">Factory</span><span class="special">::</span><span class="identifier">result_type</span> <span class="identifier">ptr</span> <span class="special">=</span> <span class="identifier">new_obj</span><span class="special">(</span><span class="identifier">a</span><span class="special">,</span><span class="identifier">b</span><span class="special">);</span>
|
||||
|
||||
<span class="comment">// again, no common base class or virtual functions needed,
|
||||
</span> <span class="comment">// we could enforce a polymorphic base by writing e.g.
|
||||
</span> <span class="comment">// boost::shared_ptr<base>
|
||||
</span> <span class="comment">// instead of
|
||||
</span> <span class="comment">// typename Factory::result_type
|
||||
</span> <span class="comment">// above.
|
||||
</span> <span class="comment">// Note that we are also free to have the type erasure happen
|
||||
</span> <span class="comment">// somewhere else (e.g. in the constructor of this function's
|
||||
</span> <span class="comment">// result type).
|
||||
</span>
|
||||
<span class="comment">// [...]
|
||||
</span><span class="special">}</span>
|
||||
|
||||
<span class="comment">// [... call do_something like above but with __factory__ instead
|
||||
</span><span class="comment">// of __value_factory__]
|
||||
</span></pre>
|
||||
<p>
|
||||
Although we might have created polymorphic objects in the previous example,
|
||||
we have used compile time polymorphism for the factory. If we want to erase
|
||||
the type of the factory and thus allow polymorphism at run time, we can use
|
||||
<a href="http://www.boost.org/doc/html/function.html" target="_top">Boost.Function</a>
|
||||
to do so. The first example can be rewritten as follows.
|
||||
</p>
|
||||
<pre class="programlisting"><span class="keyword">typedef</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">function</span><span class="special"><</span> <span class="identifier">an_abstract_class</span><span class="special">*()</span> <span class="special">></span> <span class="identifier">a_factory</span><span class="special">;</span>
|
||||
|
||||
<span class="comment">// [...]
|
||||
</span>
|
||||
<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span>
|
||||
<span class="special">{</span>
|
||||
<a href="http://www.sgi.com/tech/stl/map.html" target="_top"><code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">map</span></code></a><span class="special"><</span><a href="http://www.sgi.com/tech/stl/string.html" target="_top"><code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span></code></a><span class="special">,</span><span class="identifier">a_factory</span><span class="special">></span> <span class="identifier">factories</span><span class="special">;</span>
|
||||
|
||||
<span class="comment">// [...]
|
||||
</span>
|
||||
<span class="identifier">factories</span><span class="special">[</span><span class="string">"a_name"</span><span class="special">]</span> <span class="special">=</span> <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">factory</span></code><span class="special"><</span><span class="identifier">a_concrete_class</span><span class="special">*>();</span>
|
||||
<span class="identifier">factories</span><span class="special">[</span><span class="string">"another_name"</span><span class="special">]</span> <span class="special">=</span>
|
||||
<code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">factory</span></code><span class="special"><</span><span class="identifier">another_concrete_class</span><span class="special">*>();</span>
|
||||
|
||||
<span class="comment">// [...]
|
||||
</span><span class="special">}</span>
|
||||
</pre>
|
||||
<p>
|
||||
Of course we can just as easy create factories that take arguments and/or return
|
||||
<a href="http://www.boost.org/libs/smart_ptr/index.html" target="_top">Smart Pointers</a>.
|
||||
</p>
|
||||
</div>
|
||||
<div class="section" lang="en">
|
||||
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
|
||||
<a name="boost_functional_factory.reference"></a><a href="index.html#boost_functional_factory.reference" title=" Reference"> Reference</a></h2></div></div></div>
|
||||
<div class="toc"><dl>
|
||||
<dt><span class="section"><a href="index.html#boost_functional_factory.reference.value_factory">value_factory</a></span></dt>
|
||||
<dt><span class="section"><a href="index.html#boost_functional_factory.reference.factory">factory</a></span></dt>
|
||||
</dl></div>
|
||||
<div class="section" lang="en">
|
||||
<div class="titlepage"><div><div><h3 class="title">
|
||||
<a name="boost_functional_factory.reference.value_factory"></a><a href="index.html#boost_functional_factory.reference.value_factory" title="value_factory">value_factory</a></h3></div></div></div>
|
||||
<a name="boost_functional_factory.reference.value_factory.description"></a><h4>
|
||||
<a name="id936876"></a>
|
||||
<a href="index.html#boost_functional_factory.reference.value_factory.description">Description</a>
|
||||
</h4>
|
||||
<p>
|
||||
Function object template that invokes the constructor of the type <code class="computeroutput"><span class="identifier">T</span></code>.
|
||||
</p>
|
||||
<a name="boost_functional_factory.reference.value_factory.header"></a><h4>
|
||||
<a name="id936914"></a>
|
||||
<a href="index.html#boost_functional_factory.reference.value_factory.header">Header</a>
|
||||
</h4>
|
||||
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">functional</span><span class="special">/</span><span class="identifier">value_factory</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
|
||||
</pre>
|
||||
<a name="boost_functional_factory.reference.value_factory.synopsis"></a><h4>
|
||||
<a name="id936989"></a>
|
||||
<a href="index.html#boost_functional_factory.reference.value_factory.synopsis">Synopsis</a>
|
||||
</h4>
|
||||
<pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span>
|
||||
<span class="special">{</span>
|
||||
<span class="keyword">template</span><span class="special"><</span> <span class="keyword">typename</span> <span class="identifier">T</span> <span class="special">></span>
|
||||
<span class="keyword">class</span> <span class="identifier">value_factory</span><span class="special">;</span>
|
||||
<span class="special">}</span>
|
||||
</pre>
|
||||
<div class="variablelist">
|
||||
<p class="title"><b>Notation</b></p>
|
||||
<dl>
|
||||
<dt><span class="term"><code class="computeroutput"><span class="identifier">T</span></code></span></dt>
|
||||
<dd><p>
|
||||
an arbitrary type with at least one public constructor
|
||||
</p></dd>
|
||||
<dt><span class="term"><code class="computeroutput"><span class="identifier">a0</span></code>...<code class="computeroutput"><span class="identifier">aN</span></code></span></dt>
|
||||
<dd><p>
|
||||
argument LValues to a constructor of <code class="computeroutput"><span class="identifier">T</span></code>
|
||||
</p></dd>
|
||||
<dt><span class="term"><code class="computeroutput"><span class="identifier">F</span></code></span></dt>
|
||||
<dd><p>
|
||||
the type <code class="computeroutput"><span class="identifier">value_factory</span><span class="special"><</span><span class="identifier">F</span><span class="special">></span></code>
|
||||
</p></dd>
|
||||
<dt><span class="term"><code class="computeroutput"><span class="identifier">f</span></code></span></dt>
|
||||
<dd><p>
|
||||
an instance object of <code class="computeroutput"><span class="identifier">F</span></code>
|
||||
</p></dd>
|
||||
</dl>
|
||||
</div>
|
||||
<a name="boost_functional_factory.reference.value_factory.expression_semantics"></a><h4>
|
||||
<a name="id937226"></a>
|
||||
<a href="index.html#boost_functional_factory.reference.value_factory.expression_semantics">Expression
|
||||
Semantics</a>
|
||||
</h4>
|
||||
<div class="informaltable"><table class="table">
|
||||
<colgroup>
|
||||
<col>
|
||||
<col>
|
||||
</colgroup>
|
||||
<thead><tr>
|
||||
<th>
|
||||
<p>
|
||||
Expression
|
||||
</p>
|
||||
</th>
|
||||
<th>
|
||||
<p>
|
||||
Semantics
|
||||
</p>
|
||||
</th>
|
||||
</tr></thead>
|
||||
<tbody>
|
||||
<tr>
|
||||
<td>
|
||||
<p>
|
||||
<code class="computeroutput"><span class="identifier">F</span><span class="special">()</span></code>
|
||||
</p>
|
||||
</td>
|
||||
<td>
|
||||
<p>
|
||||
creates an object of type <code class="computeroutput"><span class="identifier">F</span></code>.
|
||||
</p>
|
||||
</td>
|
||||
</tr>
|
||||
<tr>
|
||||
<td>
|
||||
<p>
|
||||
<code class="computeroutput"><span class="identifier">F</span><span class="special">(</span><span class="identifier">f</span><span class="special">)</span></code>
|
||||
</p>
|
||||
</td>
|
||||
<td>
|
||||
<p>
|
||||
creates an object of type <code class="computeroutput"><span class="identifier">F</span></code>.
|
||||
</p>
|
||||
</td>
|
||||
</tr>
|
||||
<tr>
|
||||
<td>
|
||||
<p>
|
||||
<code class="computeroutput"><span class="identifier">f</span><span class="special">(</span><span class="identifier">a0</span></code>...<code class="computeroutput"><span class="identifier">aN</span><span class="special">)</span></code>
|
||||
</p>
|
||||
</td>
|
||||
<td>
|
||||
<p>
|
||||
returns <code class="computeroutput"><span class="identifier">T</span><span class="special">(</span><span class="identifier">a0</span></code>...<code class="computeroutput"><span class="identifier">aN</span><span class="special">)</span></code>.
|
||||
</p>
|
||||
</td>
|
||||
</tr>
|
||||
<tr>
|
||||
<td>
|
||||
<p>
|
||||
<code class="computeroutput"><span class="identifier">F</span><span class="special">::</span><span class="identifier">result_type</span></code>
|
||||
</p>
|
||||
</td>
|
||||
<td>
|
||||
<p>
|
||||
is the type <code class="computeroutput"><span class="identifier">T</span></code>.
|
||||
</p>
|
||||
</td>
|
||||
</tr>
|
||||
</tbody>
|
||||
</table></div>
|
||||
<a name="boost_functional_factory.reference.value_factory.limits"></a><h4>
|
||||
<a name="id937498"></a>
|
||||
<a href="index.html#boost_functional_factory.reference.value_factory.limits">Limits</a>
|
||||
</h4>
|
||||
<p>
|
||||
The macro BOOST_FUNCTIONAL_VALUE_FACTORY_MAX_ARITY can be defined to set
|
||||
the maximum arity. It defaults to 10.
|
||||
</p>
|
||||
</div>
|
||||
<div class="section" lang="en">
|
||||
<div class="titlepage"><div><div><h3 class="title">
|
||||
<a name="boost_functional_factory.reference.factory"></a><a href="index.html#boost_functional_factory.reference.factory" title="factory">factory</a></h3></div></div></div>
|
||||
<a name="boost_functional_factory.reference.factory.description"></a><h4>
|
||||
<a name="id937545"></a>
|
||||
<a href="index.html#boost_functional_factory.reference.factory.description">Description</a>
|
||||
</h4>
|
||||
<p>
|
||||
Function object template that dynamically constructs a pointee object for
|
||||
the type of pointer given as template argument. Smart pointers may be used
|
||||
for the template argument, given that <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">pointee</span><span class="special"><</span><span class="identifier">Pointer</span><span class="special">>::</span><span class="identifier">type</span></code>
|
||||
yields the pointee type.
|
||||
</p>
|
||||
<p>
|
||||
If an <span class="underline">_allocator</span>_ is given, it is used
|
||||
for memory allocation and the placement form of the <code class="computeroutput"><span class="keyword">new</span></code>
|
||||
operator is used to construct the object. A function object that calls the
|
||||
destructor and deallocates the memory with a copy of the Allocator is used
|
||||
for the second constructor argument of <code class="computeroutput"><span class="identifier">Pointer</span></code>
|
||||
(thus it must be a __smart<span class="underline">pointer</span>_
|
||||
that provides a suitable constructor, such as <a href="http://www.boost.org/libs/smart_ptr/shared_ptr.htm" target="_top"><code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">shared_ptr</span></code></a>).
|
||||
</p>
|
||||
<p>
|
||||
If a third template argument is <code class="computeroutput"><span class="identifier">factory_passes_alloc_to_smart_pointer</span></code>,
|
||||
the allocator itself is used for the third constructor argument of <code class="computeroutput"><span class="identifier">Pointer</span></code> (<a href="http://www.boost.org/libs/smart_ptr/shared_ptr.htm" target="_top"><code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">shared_ptr</span></code></a> then uses the allocator
|
||||
to manage the memory of its seperately allocated reference counter).
|
||||
</p>
|
||||
<a name="boost_functional_factory.reference.factory.header"></a><h4>
|
||||
<a name="id937729"></a>
|
||||
<a href="index.html#boost_functional_factory.reference.factory.header">Header</a>
|
||||
</h4>
|
||||
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">functional</span><span class="special">/</span><span class="identifier">factory</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
|
||||
</pre>
|
||||
<a name="boost_functional_factory.reference.factory.synopsis"></a><h4>
|
||||
<a name="id937804"></a>
|
||||
<a href="index.html#boost_functional_factory.reference.factory.synopsis">Synopsis</a>
|
||||
</h4>
|
||||
<pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span>
|
||||
<span class="special">{</span>
|
||||
<span class="keyword">enum</span> <span class="identifier">factory_alloc_propagation</span>
|
||||
<span class="special">{</span>
|
||||
<span class="identifier">factory_alloc_for_pointee_and_deleter</span><span class="special">,</span>
|
||||
<span class="identifier">factory_passes_alloc_to_smart_pointer</span>
|
||||
<span class="special">};</span>
|
||||
|
||||
<span class="keyword">template</span><span class="special"><</span> <span class="keyword">typename</span> <span class="identifier">Pointer</span><span class="special">,</span>
|
||||
<span class="keyword">class</span> <span class="identifier">Allocator</span> <span class="special">=</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">none_t</span><span class="special">,</span>
|
||||
<span class="identifier">factory_alloc_propagation</span> <span class="identifier">AllocProp</span> <span class="special">=</span>
|
||||
<span class="identifier">factory_alloc_for_pointee_and_deleter</span> <span class="special">></span>
|
||||
<span class="keyword">class</span> <span class="identifier">factory</span><span class="special">;</span>
|
||||
<span class="special">}</span>
|
||||
</pre>
|
||||
<div class="variablelist">
|
||||
<p class="title"><b>Notation</b></p>
|
||||
<dl>
|
||||
<dt><span class="term"><code class="computeroutput"><span class="identifier">T</span></code></span></dt>
|
||||
<dd><p>
|
||||
an arbitrary type with at least one public constructor
|
||||
</p></dd>
|
||||
<dt><span class="term"><code class="computeroutput"><span class="identifier">P</span></code></span></dt>
|
||||
<dd><p>
|
||||
pointer or smart pointer to <code class="computeroutput"><span class="identifier">T</span></code>
|
||||
</p></dd>
|
||||
<dt><span class="term"><code class="computeroutput"><span class="identifier">a0</span></code>...<code class="computeroutput"><span class="identifier">aN</span></code></span></dt>
|
||||
<dd><p>
|
||||
argument LValues to a constructor of <code class="computeroutput"><span class="identifier">T</span></code>
|
||||
</p></dd>
|
||||
<dt><span class="term"><code class="computeroutput"><span class="identifier">F</span></code></span></dt>
|
||||
<dd><p>
|
||||
the type <code class="computeroutput"><span class="identifier">factory</span><span class="special"><</span><span class="identifier">P</span><span class="special">></span></code>
|
||||
</p></dd>
|
||||
<dt><span class="term"><code class="computeroutput"><span class="identifier">f</span></code></span></dt>
|
||||
<dd><p>
|
||||
an instance object of <code class="computeroutput"><span class="identifier">F</span></code>
|
||||
</p></dd>
|
||||
</dl>
|
||||
</div>
|
||||
<a name="boost_functional_factory.reference.factory.expression_semantics"></a><h4>
|
||||
<a name="id938169"></a>
|
||||
<a href="index.html#boost_functional_factory.reference.factory.expression_semantics">Expression
|
||||
Semantics</a>
|
||||
</h4>
|
||||
<div class="informaltable"><table class="table">
|
||||
<colgroup>
|
||||
<col>
|
||||
<col>
|
||||
</colgroup>
|
||||
<thead><tr>
|
||||
<th>
|
||||
<p>
|
||||
Expression
|
||||
</p>
|
||||
</th>
|
||||
<th>
|
||||
<p>
|
||||
Semantics
|
||||
</p>
|
||||
</th>
|
||||
</tr></thead>
|
||||
<tbody>
|
||||
<tr>
|
||||
<td>
|
||||
<p>
|
||||
<code class="computeroutput"><span class="identifier">F</span><span class="special">()</span></code>
|
||||
</p>
|
||||
</td>
|
||||
<td>
|
||||
<p>
|
||||
creates an object of type <code class="computeroutput"><span class="identifier">F</span></code>.
|
||||
</p>
|
||||
</td>
|
||||
</tr>
|
||||
<tr>
|
||||
<td>
|
||||
<p>
|
||||
<code class="computeroutput"><span class="identifier">F</span><span class="special">(</span><span class="identifier">f</span><span class="special">)</span></code>
|
||||
</p>
|
||||
</td>
|
||||
<td>
|
||||
<p>
|
||||
creates an object of type <code class="computeroutput"><span class="identifier">F</span></code>.
|
||||
</p>
|
||||
</td>
|
||||
</tr>
|
||||
<tr>
|
||||
<td>
|
||||
<p>
|
||||
<code class="computeroutput"><span class="identifier">f</span><span class="special">(</span><span class="identifier">a0</span></code>...<code class="computeroutput"><span class="identifier">aN</span><span class="special">)</span></code>
|
||||
</p>
|
||||
</td>
|
||||
<td>
|
||||
<p>
|
||||
dynamically creates an object of type <code class="computeroutput"><span class="identifier">T</span></code>
|
||||
using <code class="computeroutput"><span class="identifier">a0</span></code>...<code class="computeroutput"><span class="identifier">aN</span></code> as arguments for the constructor
|
||||
invocation.
|
||||
</p>
|
||||
</td>
|
||||
</tr>
|
||||
<tr>
|
||||
<td>
|
||||
<p>
|
||||
<code class="computeroutput"><span class="identifier">F</span><span class="special">::</span><span class="identifier">result_type</span></code>
|
||||
</p>
|
||||
</td>
|
||||
<td>
|
||||
<p>
|
||||
is the type <code class="computeroutput"><span class="identifier">P</span></code> with
|
||||
top-level cv-qualifiers removed.
|
||||
</p>
|
||||
</td>
|
||||
</tr>
|
||||
</tbody>
|
||||
</table></div>
|
||||
<a name="boost_functional_factory.reference.factory.limits"></a><h4>
|
||||
<a name="id938440"></a>
|
||||
<a href="index.html#boost_functional_factory.reference.factory.limits">Limits</a>
|
||||
</h4>
|
||||
<p>
|
||||
The macro BOOST_FUNCTIONAL_FACTORY_MAX_ARITY can be defined to set the maximum
|
||||
arity. It defaults to 10.
|
||||
</p>
|
||||
</div>
|
||||
</div>
|
||||
<div class="section" lang="en">
|
||||
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
|
||||
<a name="boost_functional_factory.acknowledgements"></a><a href="index.html#boost_functional_factory.acknowledgements" title="Acknowledgements">Acknowledgements</a></h2></div></div></div>
|
||||
<p>
|
||||
Eric Niebler requested a function to invoke a type's constructor (with the
|
||||
arguments supplied as a Tuple) as a Fusion feature. These Factory utilities
|
||||
are a factored-out generalization of this idea.
|
||||
</p>
|
||||
<p>
|
||||
Dave Abrahams suggested Smart Pointer support for exception safety, providing
|
||||
useful hints for the implementation.
|
||||
</p>
|
||||
<p>
|
||||
Joel de Guzman's documentation style was copied from Fusion.
|
||||
</p>
|
||||
<p>
|
||||
Further, I want to thank Peter Dimov for sharing his insights on language details
|
||||
and their evolution.
|
||||
</p>
|
||||
</div>
|
||||
<div class="section" lang="en">
|
||||
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
|
||||
<a name="boost_functional_factory.references"></a><a href="index.html#boost_functional_factory.references" title="References">References</a></h2></div></div></div>
|
||||
<div class="orderedlist"><ol type="1">
|
||||
<li>
|
||||
<a href="http://en.wikipedia.org/wiki/Design_Patterns" target="_top">Design Patterns</a>,
|
||||
Gamma et al. - Addison Wesley Publishing, 1995
|
||||
</li>
|
||||
<li>
|
||||
<a href="http://www.sgi.com/tech/stl/" target="_top">Standard Template Library Programmer's
|
||||
Guide</a>, Hewlett-Packard Company, 1994
|
||||
</li>
|
||||
<li>
|
||||
<a href="http://www.boost.org/libs/bind/bind.html" target="_top">Boost.Bind</a>,
|
||||
Peter Dimov, 2001-2005
|
||||
</li>
|
||||
<li>
|
||||
<a href="http://www.boost.org/doc/html/function.html" target="_top">Boost.Function</a>,
|
||||
Douglas Gregor, 2001-2004
|
||||
</li>
|
||||
</ol></div>
|
||||
</div>
|
||||
</div>
|
||||
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
|
||||
<td align="left"><p><small>Last revised: November 01, 2008 at 21:44:52 GMT</small></p></td>
|
||||
<td align="right"><div class="copyright-footer"></div></td>
|
||||
</tr></table>
|
||||
<hr>
|
||||
<div class="spirit-nav"></div>
|
||||
</body>
|
||||
</html>
|
||||
21
factory/test/Jamfile
Normal file
21
factory/test/Jamfile
Normal file
@@ -0,0 +1,21 @@
|
||||
|
||||
# (C) Copyright Tobias Schwinger
|
||||
#
|
||||
# Use modification and distribution are subject to the boost Software License,
|
||||
# Version 1.0. (See http:/\/www.boost.org/LICENSE_1_0.txt).
|
||||
|
||||
import testing ;
|
||||
|
||||
project factory-tests
|
||||
: requirements
|
||||
<include>/Users/tosh/Lab/boost
|
||||
<include>/Users/tosh/Lab/deploy/x_files/factory
|
||||
;
|
||||
|
||||
test-suite functional/factory
|
||||
:
|
||||
[ run value_factory.cpp ]
|
||||
[ run factory.cpp ]
|
||||
[ run factory_with_allocator.cpp ]
|
||||
;
|
||||
|
||||
36
factory/test/factory.cpp
Normal file
36
factory/test/factory.cpp
Normal file
@@ -0,0 +1,36 @@
|
||||
/*=============================================================================
|
||||
Copyright (c) 2007 Tobias Schwinger
|
||||
|
||||
Use modification and distribution are subject to the Boost Software
|
||||
License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
|
||||
http://www.boost.org/LICENSE_1_0.txt).
|
||||
==============================================================================*/
|
||||
|
||||
#include <boost/functional/factory.hpp>
|
||||
#include <boost/detail/lightweight_test.hpp>
|
||||
|
||||
#include <memory>
|
||||
|
||||
class sum
|
||||
{
|
||||
int val_sum;
|
||||
public:
|
||||
sum(int a, int b) : val_sum(a + b) { }
|
||||
|
||||
operator int() const { return this->val_sum; }
|
||||
};
|
||||
|
||||
int main()
|
||||
{
|
||||
int one = 1, two = 2;
|
||||
{
|
||||
sum* instance( boost::factory< sum* >()(one,two) );
|
||||
BOOST_TEST(*instance == 3);
|
||||
}
|
||||
{
|
||||
std::auto_ptr<sum> instance( boost::factory< std::auto_ptr<sum> >()(one,two) );
|
||||
BOOST_TEST(*instance == 3);
|
||||
}
|
||||
return boost::report_errors();
|
||||
}
|
||||
|
||||
79
factory/test/factory_with_allocator.cpp
Normal file
79
factory/test/factory_with_allocator.cpp
Normal file
@@ -0,0 +1,79 @@
|
||||
/*=============================================================================
|
||||
Copyright (c) 2007 Tobias Schwinger
|
||||
|
||||
Use modification and distribution are subject to the Boost Software
|
||||
License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
|
||||
http://www.boost.org/LICENSE_1_0.txt).
|
||||
==============================================================================*/
|
||||
|
||||
#include <boost/functional/factory.hpp>
|
||||
#include <boost/detail/lightweight_test.hpp>
|
||||
|
||||
#include <cstddef>
|
||||
#include <memory>
|
||||
#include <boost/shared_ptr.hpp>
|
||||
|
||||
using std::size_t;
|
||||
|
||||
class sum
|
||||
{
|
||||
int val_sum;
|
||||
public:
|
||||
sum(int a, int b) : val_sum(a + b) { }
|
||||
|
||||
operator int() const { return this->val_sum; }
|
||||
};
|
||||
|
||||
template< typename T >
|
||||
class counting_allocator : public std::allocator<T>
|
||||
{
|
||||
public:
|
||||
counting_allocator()
|
||||
{ }
|
||||
|
||||
template< typename OtherT >
|
||||
struct rebind { typedef counting_allocator<OtherT> other; };
|
||||
|
||||
template< typename OtherT >
|
||||
counting_allocator(counting_allocator<OtherT> const& that)
|
||||
{ }
|
||||
|
||||
static size_t n_allocated;
|
||||
T* allocate(size_t n, void const* hint = 0l)
|
||||
{
|
||||
n_allocated += 1;
|
||||
return std::allocator<T>::allocate(n,hint);
|
||||
}
|
||||
|
||||
static size_t n_deallocated;
|
||||
void deallocate(T* ptr, size_t n)
|
||||
{
|
||||
n_deallocated += 1;
|
||||
return std::allocator<T>::deallocate(ptr,n);
|
||||
}
|
||||
};
|
||||
template< typename T > size_t counting_allocator<T>::n_allocated = 0;
|
||||
template< typename T > size_t counting_allocator<T>::n_deallocated = 0;
|
||||
|
||||
int main()
|
||||
{
|
||||
int one = 1, two = 2;
|
||||
{
|
||||
boost::shared_ptr<sum> instance(
|
||||
boost::factory< boost::shared_ptr<sum>, counting_allocator<void>,
|
||||
boost::factory_alloc_for_pointee_and_deleter >()(one,two) );
|
||||
BOOST_TEST(*instance == 3);
|
||||
}
|
||||
BOOST_TEST(counting_allocator<sum>::n_allocated == 1);
|
||||
BOOST_TEST(counting_allocator<sum>::n_deallocated == 1);
|
||||
{
|
||||
boost::shared_ptr<sum> instance(
|
||||
boost::factory< boost::shared_ptr<sum>, counting_allocator<void>,
|
||||
boost::factory_passes_alloc_to_smart_pointer >()(one,two) );
|
||||
BOOST_TEST(*instance == 3);
|
||||
}
|
||||
BOOST_TEST(counting_allocator<sum>::n_allocated == 2);
|
||||
BOOST_TEST(counting_allocator<sum>::n_deallocated == 2);
|
||||
return boost::report_errors();
|
||||
}
|
||||
|
||||
29
factory/test/value_factory.cpp
Normal file
29
factory/test/value_factory.cpp
Normal file
@@ -0,0 +1,29 @@
|
||||
/*=============================================================================
|
||||
Copyright (c) 2007 Tobias Schwinger
|
||||
|
||||
Use modification and distribution are subject to the Boost Software
|
||||
License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
|
||||
http://www.boost.org/LICENSE_1_0.txt).
|
||||
==============================================================================*/
|
||||
|
||||
#include <boost/functional/value_factory.hpp>
|
||||
#include <boost/detail/lightweight_test.hpp>
|
||||
|
||||
class sum
|
||||
{
|
||||
int val_sum;
|
||||
public:
|
||||
sum(int a, int b) : val_sum(a + b) { }
|
||||
operator int() const { return this->val_sum; }
|
||||
};
|
||||
|
||||
int main()
|
||||
{
|
||||
int one = 1, two = 2;
|
||||
{
|
||||
sum instance( boost::value_factory< sum >()(one,two) );
|
||||
BOOST_TEST(instance == 3);
|
||||
}
|
||||
return boost::report_errors();
|
||||
}
|
||||
|
||||
19
forward/doc/Jamfile
Normal file
19
forward/doc/Jamfile
Normal file
@@ -0,0 +1,19 @@
|
||||
|
||||
# (C) Copyright Tobias Schwinger
|
||||
#
|
||||
# Use modification and distribution are subject to the boost Software License,
|
||||
# Version 1.0. (See http:/\/www.boost.org/LICENSE_1_0.txt).
|
||||
|
||||
using quickbook ;
|
||||
|
||||
xml forward : forward.qbk ;
|
||||
boostbook standalone : forward
|
||||
:
|
||||
<xsl:param>boost.root=../../../../..
|
||||
<xsl:param>boost.libraries=../../../../libraries.htm
|
||||
<xsl:param>chunk.section.depth=0
|
||||
<xsl:param>chunk.first.sections=0
|
||||
<xsl:param>generate.section.toc.level=2
|
||||
<xsl:param>toc.max.depth=1
|
||||
;
|
||||
|
||||
316
forward/doc/forward.qbk
Normal file
316
forward/doc/forward.qbk
Normal file
@@ -0,0 +1,316 @@
|
||||
[library Boost.Functional/Forward
|
||||
[quickbook 1.3]
|
||||
[version 1.0]
|
||||
[authors [Schwinger, Tobias]]
|
||||
[copyright 2007 2008 Tobias Schwinger]
|
||||
[license
|
||||
Distributed under the Boost Software License, Version 1.0.
|
||||
(See accompanying file LICENSE_1_0.txt or copy at
|
||||
[@http://www.boost.org/LICENSE_1_0.txt])
|
||||
]
|
||||
[purpose Function object adapters for generic argument forwarding.]
|
||||
[category higher-order]
|
||||
[category generic]
|
||||
[last-revision $Date: 2008/11/01 19:58:50 $]
|
||||
]
|
||||
|
||||
[def __unspecified__ /unspecified/]
|
||||
[def __boost_ref__ [@http://www.boost.org/doc/html/ref.html Boost.Ref]]
|
||||
[def __boost_result_of__ [@http://www.boost.org/libs/utility/utility.htm#result_of Boost.ResultOf]]
|
||||
[def __boost__result_of__ [@http://www.boost.org/libs/utility/utility.htm#result_of `boost::result_of`]]
|
||||
[def __the_forwarding_problem__ [@http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2002/n1385.htm The Forwarding Problem]]
|
||||
[def __boost_fusion__ [@http://www.boost.org/libs/fusion/doc/html/index.html Boost.Fusion]]
|
||||
|
||||
[section Brief Description]
|
||||
|
||||
`boost::forward_adapter` provides a reusable adapter template for function
|
||||
objects. It forwards RValues as references to const, while leaving LValues
|
||||
as-is.
|
||||
|
||||
struct g // function object that only accept LValues
|
||||
{
|
||||
template< typename T0, typename T1, typename T2 >
|
||||
void operator()(T0 & t0, T1 & t1, T2 & t2) const;
|
||||
|
||||
typedef void result_type;
|
||||
};
|
||||
|
||||
// Adapted version also accepts RValues and forwards
|
||||
// them as references to const, LValues as-is
|
||||
typedef boost::forward_adapter<g> f;
|
||||
|
||||
Another adapter, `boost::lighweight_forward_adapter` allows forwarding with
|
||||
some help from the user accepting and unwrapping reference wrappers (see
|
||||
__boost_ref__) for reference arguments, const qualifying all other arguments.
|
||||
|
||||
The target functions must be compatible with __boost_result_of__, and so are
|
||||
the adapters.
|
||||
|
||||
[endsect]
|
||||
|
||||
[section Background]
|
||||
|
||||
Let's suppose we have some function `f` that we can call like this:
|
||||
|
||||
f(123,a_variable);
|
||||
|
||||
Now we want to write another, generic function `g` that can be called the
|
||||
same way and returns some object that calls `f` with the same arguments.
|
||||
|
||||
f(123,a_variable) == g(f,123,a_variable).call_f()
|
||||
|
||||
[heading Why would we want to do it, anyway?]
|
||||
|
||||
Maybe we want to run `f` several times. Or maybe we want to run it within
|
||||
another thread. Maybe we just want to encapsulate the call expression for now,
|
||||
and then use it with other code that allows to compose more complex expressions
|
||||
in order to decompose it with C++ templates and have the compiler generate some
|
||||
machinery that eventually calls `f` at runtime (in other words; apply a
|
||||
technique that is commonly referred to as Expression Templates).
|
||||
|
||||
[heading Now, how do we do it?]
|
||||
|
||||
The bad news is: It's impossible.
|
||||
|
||||
That is so because there is a slight difference between a variable and an
|
||||
expression that evaluates to its value: Given
|
||||
|
||||
int y;
|
||||
int const z = 0;
|
||||
|
||||
and
|
||||
|
||||
template< typename T > void func1(T & x);
|
||||
|
||||
we can call
|
||||
|
||||
func1(y); // x is a reference to a non-const object
|
||||
func1(z); // x is a reference to a const object
|
||||
|
||||
where
|
||||
|
||||
func1(1); // fails to compile.
|
||||
|
||||
This way we can safely have `func1` store its reference argument and the
|
||||
compiler keeps us from storing a reference to an object with temporary lifetime.
|
||||
|
||||
It is important to realize that non-constness and whether an object binds to a
|
||||
non-const reference parameter are two different properties. The latter is the
|
||||
distinction between LValues and RValues. The names stem from the left hand side
|
||||
and the right hand side of assignment expressions, thus LValues are typically
|
||||
the ones you can assign to, and RValues the temporary results from the right
|
||||
hand side expression.
|
||||
|
||||
y = 1+2; // a is LValue, 1+2 is the expression producing the RValue,
|
||||
// 1+2 = a; // usually makes no sense.
|
||||
|
||||
func1(y); // works, because y is an LValue
|
||||
// func1(1+2); // fails to compile, because we only got an RValue.
|
||||
|
||||
If we add const qualification on the parameter, our function also accepts
|
||||
RValues:
|
||||
|
||||
template< typename T > void func2(T const & x);
|
||||
|
||||
// [...] function scope:
|
||||
func2(1); // x is a reference to a const temporary, object,
|
||||
func2(y); // x is a reference to a const object, while y is not const, and
|
||||
func2(z); // x is a reference to a const object, just like z.
|
||||
|
||||
In all cases, the argument `x` in `func2` is a const-qualified LValue.
|
||||
We can use function overloading to identify non-const LValues:
|
||||
|
||||
template< typename T > void func3(T const & x); // #1
|
||||
template< typename T > void func3(T & x); // #2
|
||||
|
||||
// [...] function scope:
|
||||
func3(1); // x is a reference to a const, temporary object in #1,
|
||||
func3(y); // x is a reference to a non-const object in #2, and
|
||||
func3(z); // x is a reference to a const object in #1.
|
||||
|
||||
Note that all arguments `x` in the overloaded function `func3` are LValues.
|
||||
In fact, there is no way to transport RValues into a function as-is in C++98.
|
||||
Also note that we can't distinguish between what used to be a const qualified
|
||||
LValue and an RValue.
|
||||
|
||||
That's as close as we can get to a generic forwarding function `g` as
|
||||
described above by the means of C++ 98. See __the_forwarding_problem__ for a
|
||||
very detailed discussion including solutions that require language changes.
|
||||
|
||||
Now, for actually implementing it, we need 2^N overloads for N parameters
|
||||
(each with and without const qualifier) for each number of arguments
|
||||
(that is 2^(Nmax+1) - 2^Nmin). Right, that means the compile-time complexity
|
||||
is O(2^N), however the factor is low so it works quite well for a reasonable
|
||||
number (< 10) of arguments.
|
||||
|
||||
[endsect]
|
||||
|
||||
[section:reference Reference]
|
||||
|
||||
[section forward_adapter]
|
||||
|
||||
[heading Description]
|
||||
|
||||
Function object adapter template whose instances are callable with LValue and
|
||||
RValue arguments. RValue arguments are forwarded as reference-to-const typed
|
||||
LValues.
|
||||
|
||||
An arity can be given as second, numeric non-type template argument to restrict
|
||||
forwarding to a specific arity.
|
||||
If a third, numeric non-type template argument is present, the second and third
|
||||
template argument are treated as minimum and maximum arity, respectively.
|
||||
Specifying an arity can be helpful to improve the readability of diagnostic
|
||||
messages and compile time performance.
|
||||
|
||||
__boost_result_of__ can be used to determine the result types of specific call
|
||||
expressions.
|
||||
|
||||
[heading Header]
|
||||
#include <boost/functional/forward_adapter.hpp>
|
||||
|
||||
[heading Synopsis]
|
||||
|
||||
namespace boost
|
||||
{
|
||||
template< class Function,
|
||||
int Arity_Or_MinArity = __unspecified__, int MaxArity = __unspecified__ >
|
||||
class forward_adapter;
|
||||
}
|
||||
|
||||
[variablelist Notation
|
||||
[[`F`] [a possibly const qualified function object type or reference type thereof]]
|
||||
[[`f`] [an object convertible to `F`]]
|
||||
[[`FA`] [the type `forward_adapter<F>`]]
|
||||
[[`fa`] [an instance object of `FA`, initialized with `f`]]
|
||||
[[`a0`...`aN`] [arguments to `fa`]]
|
||||
]
|
||||
|
||||
The result type of a target function invocation must be
|
||||
|
||||
__boost__result_of__<F*(TA0 [const]&...TAN [const]&])>::type
|
||||
|
||||
where `TA0`...`TAN` denote the argument types of `a0`...`aN`.
|
||||
|
||||
[heading Expression Semantics]
|
||||
|
||||
[table
|
||||
[[Expression] [Semantics]]
|
||||
[[`FA(f)`] [creates an adapter, initializes the target function with `f`.]]
|
||||
[[`FA()`] [creates an adapter, attempts to use `F`'s default constructor.]]
|
||||
[[`fa(a0`...`aN)`] [calls `f` with with arguments `a0`...`aN`.]]
|
||||
]
|
||||
|
||||
[heading Limits]
|
||||
|
||||
The macro BOOST_FUNCTIONAL_FORWARD_ADAPTER_MAX_ARITY can be defined to set the
|
||||
maximum call arity. It defaults to 6.
|
||||
|
||||
[heading Complexity]
|
||||
|
||||
Preprocessing time: O(2^N), where N is the arity limit.
|
||||
Compile time: O(2^N), where N depends on the arity range.
|
||||
Run time: O(0) if the compiler inlines, O(1) otherwise.
|
||||
|
||||
[endsect]
|
||||
|
||||
|
||||
[section lightweight_forward_adapter]
|
||||
|
||||
[heading Description]
|
||||
|
||||
Function object adapter template whose instances are callable with LValue and
|
||||
RValue arguments. All arguments are forwarded as reference-to-const typed
|
||||
LValues, except for reference wrappers which are unwrapped and may yield
|
||||
non-const LValues.
|
||||
|
||||
An arity can be given as second, numeric non-type template argument to restrict
|
||||
forwarding to a specific arity.
|
||||
If a third, numeric non-type template argument is present, the second and third
|
||||
template argument are treated as minimum and maximum arity, respectively.
|
||||
Specifying an arity can be helpful to improve the readability of diagnostic
|
||||
messages and compile time performance.
|
||||
|
||||
__boost_result_of__ can be used to determine the result types of specific call
|
||||
expressions.
|
||||
|
||||
[heading Header]
|
||||
#include <boost/functional/lightweight_forward_adapter.hpp>
|
||||
|
||||
[heading Synopsis]
|
||||
|
||||
namespace boost
|
||||
{
|
||||
template< class Function,
|
||||
int Arity_Or_MinArity = __unspecified__, int MaxArity = __unspecified__ >
|
||||
struct lightweight_forward_adapter;
|
||||
}
|
||||
|
||||
[variablelist Notation
|
||||
[[`F`] [a possibly const qualified function object type or reference type thereof]]
|
||||
[[`f`] [an object convertible to `F`]]
|
||||
[[`FA`] [the type `lightweight_forward_adapter<F>`]]
|
||||
[[`fa`] [an instance of `FA`, initialized with `f`]]
|
||||
[[`a0`...`aN`] [arguments to `fa`]]
|
||||
]
|
||||
|
||||
The result type of a target function invocation must be
|
||||
|
||||
__boost__result_of__<F*(TA0 [const]&...TAN [const]&])>::type
|
||||
|
||||
where `TA0`...`TAN` denote the argument types of `a0`...`aN`.
|
||||
|
||||
[heading Expression Semantics]
|
||||
|
||||
[table
|
||||
[[Expression] [Semantics]]
|
||||
[[`FA(f)`] [creates an adapter, initializes the target function with `f`.]]
|
||||
[[`FA()`] [creates an adapter, attempts to use `F`'s default constructor.]]
|
||||
[[`fa(a0`...`aN)`] [calls `f` with with const arguments `a0`...`aN`. If `aI` is a
|
||||
reference wrapper it is unwrapped.]]
|
||||
]
|
||||
|
||||
[heading Limits]
|
||||
|
||||
The macro BOOST_FUNCTIONAL_LIGHTWEIGHT_FORWARD_ADAPTER_MAX_ARITY can be defined
|
||||
to set the maximum call arity. It defaults to 10.
|
||||
|
||||
[heading Complexity]
|
||||
|
||||
Preprocessing time: O(N), where N is the arity limit.
|
||||
Compile time: O(N), where N is the effective arity of a call.
|
||||
Run time: O(0) if the compiler inlines, O(1) otherwise.
|
||||
|
||||
[endsect]
|
||||
|
||||
[endsect]
|
||||
|
||||
|
||||
[section Acknowledgements]
|
||||
|
||||
As these utilities are factored out of the __boost_fusion__ functional module,
|
||||
I want to thank Dan Marsden and Joel de Guzman for letting me participate in the
|
||||
development of that great library in the first place.
|
||||
|
||||
Further, I want to credit the authors of the references below, for their
|
||||
in-depth investigation of the problem and the solution implemented here.
|
||||
|
||||
Last but not least I want to thank Vesa Karnoven and Paul Mensonides for the
|
||||
Boost Preprocessor library. Without it, I would have ended up with an external
|
||||
code generator for this one.
|
||||
|
||||
[endsect]
|
||||
|
||||
|
||||
[section References]
|
||||
|
||||
# [@http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2002/n1385.htm The Forwarding Problem],
|
||||
Peter Dimov, Howard E. Hinnant, David Abrahams, 2002
|
||||
|
||||
# [@http://www.boost.org/libs/utility/utility.htm#result_of Boost.ResultOf],
|
||||
Douglas Gregor, 2004
|
||||
|
||||
# [@http://www.boost.org/doc/html/ref.html Boost.Ref],
|
||||
Jaakko Jarvi, Peter Dimov, Douglas Gregor, David Abrahams, 1999-2002
|
||||
|
||||
[endsect]
|
||||
|
||||
528
forward/doc/html/boostbook.css
Normal file
528
forward/doc/html/boostbook.css
Normal file
@@ -0,0 +1,528 @@
|
||||
/*=============================================================================
|
||||
Copyright (c) 2004 Joel de Guzman
|
||||
http://spirit.sourceforge.net/
|
||||
|
||||
Use, modification and distribution is subject to the Boost Software
|
||||
License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
|
||||
http://www.boost.org/LICENSE_1_0.txt)
|
||||
=============================================================================*/
|
||||
|
||||
/*=============================================================================
|
||||
Body defaults
|
||||
=============================================================================*/
|
||||
|
||||
body
|
||||
{
|
||||
margin: 1em;
|
||||
font-family: sans-serif;
|
||||
}
|
||||
|
||||
/*=============================================================================
|
||||
Paragraphs
|
||||
=============================================================================*/
|
||||
|
||||
p
|
||||
{
|
||||
text-align: left;
|
||||
font-size: 10pt;
|
||||
line-height: 1.15;
|
||||
}
|
||||
|
||||
/*=============================================================================
|
||||
Program listings
|
||||
=============================================================================*/
|
||||
|
||||
/* Code on paragraphs */
|
||||
p tt.computeroutput
|
||||
{
|
||||
font-size: 9pt;
|
||||
}
|
||||
|
||||
pre.synopsis
|
||||
{
|
||||
font-size: 90%;
|
||||
margin: 1pc 4% 0pc 4%;
|
||||
padding: 0.5pc 0.5pc 0.5pc 0.5pc;
|
||||
}
|
||||
|
||||
.programlisting,
|
||||
.screen
|
||||
{
|
||||
font-size: 9pt;
|
||||
display: block;
|
||||
margin: 1pc 4% 0pc 4%;
|
||||
padding: 0.5pc 0.5pc 0.5pc 0.5pc;
|
||||
}
|
||||
|
||||
/* Program listings in tables don't get borders */
|
||||
td .programlisting,
|
||||
td .screen
|
||||
{
|
||||
margin: 0pc 0pc 0pc 0pc;
|
||||
padding: 0pc 0pc 0pc 0pc;
|
||||
}
|
||||
|
||||
/*=============================================================================
|
||||
Headings
|
||||
=============================================================================*/
|
||||
|
||||
h1, h2, h3, h4, h5, h6
|
||||
{
|
||||
text-align: left;
|
||||
margin: 1em 0em 0.5em 0em;
|
||||
font-weight: bold;
|
||||
}
|
||||
|
||||
h1 { font: 140% }
|
||||
h2 { font: bold 140% }
|
||||
h3 { font: bold 130% }
|
||||
h4 { font: bold 120% }
|
||||
h5 { font: italic 110% }
|
||||
h6 { font: italic 100% }
|
||||
|
||||
/* Top page titles */
|
||||
title,
|
||||
h1.title,
|
||||
h2.title
|
||||
h3.title,
|
||||
h4.title,
|
||||
h5.title,
|
||||
h6.title,
|
||||
.refentrytitle
|
||||
{
|
||||
font-weight: bold;
|
||||
margin-bottom: 1pc;
|
||||
}
|
||||
|
||||
h1.title { font-size: 140% }
|
||||
h2.title { font-size: 140% }
|
||||
h3.title { font-size: 130% }
|
||||
h4.title { font-size: 120% }
|
||||
h5.title { font-size: 110% }
|
||||
h6.title { font-size: 100% }
|
||||
|
||||
.section h1
|
||||
{
|
||||
margin: 0em 0em 0.5em 0em;
|
||||
font-size: 140%;
|
||||
}
|
||||
|
||||
.section h2 { font-size: 140% }
|
||||
.section h3 { font-size: 130% }
|
||||
.section h4 { font-size: 120% }
|
||||
.section h5 { font-size: 110% }
|
||||
.section h6 { font-size: 100% }
|
||||
|
||||
/* Code on titles */
|
||||
h1 tt.computeroutput { font-size: 140% }
|
||||
h2 tt.computeroutput { font-size: 140% }
|
||||
h3 tt.computeroutput { font-size: 130% }
|
||||
h4 tt.computeroutput { font-size: 120% }
|
||||
h5 tt.computeroutput { font-size: 110% }
|
||||
h6 tt.computeroutput { font-size: 100% }
|
||||
|
||||
/*=============================================================================
|
||||
Author
|
||||
=============================================================================*/
|
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|
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564
forward/doc/html/index.html
Normal file
564
forward/doc/html/index.html
Normal file
@@ -0,0 +1,564 @@
|
||||
<html>
|
||||
<head>
|
||||
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
|
||||
<title>Chapter<EFBFBD>1.<2E>Boost.Functional/Forward 1.0</title>
|
||||
<link rel="stylesheet" href="boostbook.css" type="text/css">
|
||||
<meta name="generator" content="DocBook XSL Stylesheets V1.68.1">
|
||||
<link rel="start" href="index.html" title="Chapter<65>1.<2E>Boost.Functional/Forward 1.0">
|
||||
</head>
|
||||
<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
|
||||
<table cellpadding="2" width="100%"><tr>
|
||||
<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../boost.png"></td>
|
||||
<td align="center"><a href="../../../../../index.html">Home</a></td>
|
||||
<td align="center"><a href="../../../../libraries.htm">Libraries</a></td>
|
||||
<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
|
||||
<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
|
||||
<td align="center"><a href="../../../../../more/index.htm">More</a></td>
|
||||
</tr></table>
|
||||
<hr>
|
||||
<div class="spirit-nav"></div>
|
||||
<div class="chapter" lang="en">
|
||||
<div class="titlepage"><div>
|
||||
<div><h2 class="title">
|
||||
<a name="boost_functional_forward"></a>Chapter<EFBFBD>1.<2E>Boost.Functional/Forward 1.0</h2></div>
|
||||
<div><div class="author"><h3 class="author">
|
||||
<span class="firstname">Tobias</span> <span class="surname">Schwinger</span>
|
||||
</h3></div></div>
|
||||
<div><p class="copyright">Copyright <20> 2007, 2008 Tobias Schwinger</p></div>
|
||||
<div><div class="legalnotice">
|
||||
<a name="id934161"></a><p>
|
||||
Distributed under the Boost Software License, Version 1.0. (See accompanying
|
||||
file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
|
||||
</p>
|
||||
</div></div>
|
||||
</div></div>
|
||||
<div class="toc">
|
||||
<p><b>Table of Contents</b></p>
|
||||
<dl>
|
||||
<dt><span class="section"><a href="index.html#boost_functional_forward.brief_description">Brief Description</a></span></dt>
|
||||
<dt><span class="section"><a href="index.html#boost_functional_forward.background">Background</a></span></dt>
|
||||
<dt><span class="section"><a href="index.html#boost_functional_forward.reference"> Reference</a></span></dt>
|
||||
<dt><span class="section"><a href="index.html#boost_functional_forward.acknowledgements">Acknowledgements</a></span></dt>
|
||||
<dt><span class="section"><a href="index.html#boost_functional_forward.references">References</a></span></dt>
|
||||
</dl>
|
||||
</div>
|
||||
<div class="section" lang="en">
|
||||
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
|
||||
<a name="boost_functional_forward.brief_description"></a><a href="index.html#boost_functional_forward.brief_description" title="Brief Description">Brief Description</a></h2></div></div></div>
|
||||
<p>
|
||||
<code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">forward_adapter</span></code> provides a reusable adapter
|
||||
template for function objects. It forwards RValues as references to const,
|
||||
while leaving LValues as-is.
|
||||
</p>
|
||||
<pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">g</span> <span class="comment">// function object that only accept LValues
|
||||
</span><span class="special">{</span>
|
||||
<span class="keyword">template</span><span class="special"><</span> <span class="keyword">typename</span> <span class="identifier">T0</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">T1</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">T2</span> <span class="special">></span>
|
||||
<span class="keyword">void</span> <span class="keyword">operator</span><span class="special">()(</span><span class="identifier">T0</span> <span class="special">&</span> <span class="identifier">t0</span><span class="special">,</span> <span class="identifier">T1</span> <span class="special">&</span> <span class="identifier">t1</span><span class="special">,</span> <span class="identifier">T2</span> <span class="special">&</span> <span class="identifier">t2</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span>
|
||||
|
||||
<span class="keyword">typedef</span> <span class="keyword">void</span> <span class="identifier">result_type</span><span class="special">;</span>
|
||||
<span class="special">};</span>
|
||||
|
||||
<span class="comment">// Adapted version also accepts RValues and forwards
|
||||
</span><span class="comment">// them as references to const, LValues as-is
|
||||
</span><span class="keyword">typedef</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">forward_adapter</span><span class="special"><</span><span class="identifier">g</span><span class="special">></span> <span class="identifier">f</span><span class="special">;</span>
|
||||
</pre>
|
||||
<p>
|
||||
Another adapter, <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">lighweight_forward_adapter</span></code> allows forwarding
|
||||
with some help from the user accepting and unwrapping reference wrappers (see
|
||||
<a href="http://www.boost.org/doc/html/ref.html" target="_top">Boost.Ref</a>) for
|
||||
reference arguments, const qualifying all other arguments.
|
||||
</p>
|
||||
<p>
|
||||
The target functions must be compatible with <a href="http://www.boost.org/libs/utility/utility.htm#result_of" target="_top">Boost.ResultOf</a>,
|
||||
and so are the adapters.
|
||||
</p>
|
||||
</div>
|
||||
<div class="section" lang="en">
|
||||
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
|
||||
<a name="boost_functional_forward.background"></a><a href="index.html#boost_functional_forward.background" title="Background">Background</a></h2></div></div></div>
|
||||
<p>
|
||||
Let's suppose we have some function <code class="computeroutput"><span class="identifier">f</span></code>
|
||||
that we can call like this:
|
||||
</p>
|
||||
<pre class="programlisting"><span class="identifier">f</span><span class="special">(</span><span class="number">123</span><span class="special">,</span><span class="identifier">a_variable</span><span class="special">);</span>
|
||||
</pre>
|
||||
<p>
|
||||
Now we want to write another, generic function <code class="computeroutput"><span class="identifier">g</span></code>
|
||||
that can be called the same way and returns some object that calls <code class="computeroutput"><span class="identifier">f</span></code> with the same arguments.
|
||||
</p>
|
||||
<pre class="programlisting"><span class="identifier">f</span><span class="special">(</span><span class="number">123</span><span class="special">,</span><span class="identifier">a_variable</span><span class="special">)</span> <span class="special">==</span> <span class="identifier">g</span><span class="special">(</span><span class="identifier">f</span><span class="special">,</span><span class="number">123</span><span class="special">,</span><span class="identifier">a_variable</span><span class="special">).</span><span class="identifier">call_f</span><span class="special">()</span>
|
||||
</pre>
|
||||
<a name="boost_functional_forward.background.why_would_we_want_to_do_it__anyway_"></a><h3>
|
||||
<a name="id934701"></a>
|
||||
<a href="index.html#boost_functional_forward.background.why_would_we_want_to_do_it__anyway_">Why
|
||||
would we want to do it, anyway?</a>
|
||||
</h3>
|
||||
<p>
|
||||
Maybe we want to run <code class="computeroutput"><span class="identifier">f</span></code> several
|
||||
times. Or maybe we want to run it within another thread. Maybe we just want
|
||||
to encapsulate the call expression for now, and then use it with other code
|
||||
that allows to compose more complex expressions in order to decompose it with
|
||||
C++ templates and have the compiler generate some machinery that eventually
|
||||
calls <code class="computeroutput"><span class="identifier">f</span></code> at runtime (in other
|
||||
words; apply a technique that is commonly referred to as Expression Templates).
|
||||
</p>
|
||||
<a name="boost_functional_forward.background.now__how_do_we_do_it_"></a><h3>
|
||||
<a name="id934755"></a>
|
||||
<a href="index.html#boost_functional_forward.background.now__how_do_we_do_it_">Now,
|
||||
how do we do it?</a>
|
||||
</h3>
|
||||
<p>
|
||||
The bad news is: It's impossible.
|
||||
</p>
|
||||
<p>
|
||||
That is so because there is a slight difference between a variable and an expression
|
||||
that evaluates to its value: Given
|
||||
</p>
|
||||
<pre class="programlisting"><span class="keyword">int</span> <span class="identifier">y</span><span class="special">;</span>
|
||||
<span class="keyword">int</span> <span class="keyword">const</span> <span class="identifier">z</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span>
|
||||
</pre>
|
||||
<p>
|
||||
and
|
||||
</p>
|
||||
<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span> <span class="keyword">typename</span> <span class="identifier">T</span> <span class="special">></span> <span class="keyword">void</span> <span class="identifier">func1</span><span class="special">(</span><span class="identifier">T</span> <span class="special">&</span> <span class="identifier">x</span><span class="special">);</span>
|
||||
</pre>
|
||||
<p>
|
||||
we can call
|
||||
</p>
|
||||
<pre class="programlisting"><span class="identifier">func1</span><span class="special">(</span><span class="identifier">y</span><span class="special">);</span> <span class="comment">// x is a reference to a non-const object
|
||||
</span><span class="identifier">func1</span><span class="special">(</span><span class="identifier">z</span><span class="special">);</span> <span class="comment">// x is a reference to a const object
|
||||
</span></pre>
|
||||
<p>
|
||||
where
|
||||
</p>
|
||||
<pre class="programlisting"><span class="identifier">func1</span><span class="special">(</span><span class="number">1</span><span class="special">);</span> <span class="comment">// fails to compile.
|
||||
</span></pre>
|
||||
<p>
|
||||
This way we can safely have <code class="computeroutput"><span class="identifier">func1</span></code>
|
||||
store its reference argument and the compiler keeps us from storing a reference
|
||||
to an object with temporary lifetime.
|
||||
</p>
|
||||
<p>
|
||||
It is important to realize that non-constness and whether an object binds to
|
||||
a non-const reference parameter are two different properties. The latter is
|
||||
the distinction between LValues and RValues. The names stem from the left hand
|
||||
side and the right hand side of assignment expressions, thus LValues are typically
|
||||
the ones you can assign to, and RValues the temporary results from the right
|
||||
hand side expression.
|
||||
</p>
|
||||
<pre class="programlisting"><span class="identifier">y</span> <span class="special">=</span> <span class="number">1</span><span class="special">+</span><span class="number">2</span><span class="special">;</span> <span class="comment">// a is LValue, 1+2 is the expression producing the RValue,
|
||||
</span><span class="comment">// 1+2 = a; // usually makes no sense.
|
||||
</span>
|
||||
<span class="identifier">func1</span><span class="special">(</span><span class="identifier">y</span><span class="special">);</span> <span class="comment">// works, because y is an LValue
|
||||
</span><span class="comment">// func1(1+2); // fails to compile, because we only got an RValue.
|
||||
</span></pre>
|
||||
<p>
|
||||
If we add const qualification on the parameter, our function also accepts RValues:
|
||||
</p>
|
||||
<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span> <span class="keyword">typename</span> <span class="identifier">T</span> <span class="special">></span> <span class="keyword">void</span> <span class="identifier">func2</span><span class="special">(</span><span class="identifier">T</span> <span class="keyword">const</span> <span class="special">&</span> <span class="identifier">x</span><span class="special">);</span>
|
||||
|
||||
<span class="comment">// [...] function scope:
|
||||
</span><span class="identifier">func2</span><span class="special">(</span><span class="number">1</span><span class="special">);</span> <span class="comment">// x is a reference to a const temporary, object,
|
||||
</span><span class="identifier">func2</span><span class="special">(</span><span class="identifier">y</span><span class="special">);</span> <span class="comment">// x is a reference to a const object, while y is not const, and
|
||||
</span><span class="identifier">func2</span><span class="special">(</span><span class="identifier">z</span><span class="special">);</span> <span class="comment">// x is a reference to a const object, just like z.
|
||||
</span></pre>
|
||||
<p>
|
||||
In all cases, the argument <code class="computeroutput"><span class="identifier">x</span></code>
|
||||
in <code class="computeroutput"><span class="identifier">func2</span></code> is a const-qualified
|
||||
LValue. We can use function overloading to identify non-const LValues:
|
||||
</p>
|
||||
<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span> <span class="keyword">typename</span> <span class="identifier">T</span> <span class="special">></span> <span class="keyword">void</span> <span class="identifier">func3</span><span class="special">(</span><span class="identifier">T</span> <span class="keyword">const</span> <span class="special">&</span> <span class="identifier">x</span><span class="special">);</span> <span class="comment">// #1
|
||||
</span><span class="keyword">template</span><span class="special"><</span> <span class="keyword">typename</span> <span class="identifier">T</span> <span class="special">></span> <span class="keyword">void</span> <span class="identifier">func3</span><span class="special">(</span><span class="identifier">T</span> <span class="special">&</span> <span class="identifier">x</span><span class="special">);</span> <span class="comment">// #2
|
||||
</span>
|
||||
<span class="comment">// [...] function scope:
|
||||
</span><span class="identifier">func3</span><span class="special">(</span><span class="number">1</span><span class="special">);</span> <span class="comment">// x is a reference to a const, temporary object in #1,
|
||||
</span><span class="identifier">func3</span><span class="special">(</span><span class="identifier">y</span><span class="special">);</span> <span class="comment">// x is a reference to a non-const object in #2, and
|
||||
</span><span class="identifier">func3</span><span class="special">(</span><span class="identifier">z</span><span class="special">);</span> <span class="comment">// x is a reference to a const object in #1.
|
||||
</span></pre>
|
||||
<p>
|
||||
Note that all arguments <code class="computeroutput"><span class="identifier">x</span></code> in
|
||||
the overloaded function <code class="computeroutput"><span class="identifier">func3</span></code>
|
||||
are LValues. In fact, there is no way to transport RValues into a function
|
||||
as-is in C++98. Also note that we can't distinguish between what used to be
|
||||
a const qualified LValue and an RValue.
|
||||
</p>
|
||||
<p>
|
||||
That's as close as we can get to a generic forwarding function <code class="computeroutput"><span class="identifier">g</span></code> as described above by the means of C++
|
||||
98. See <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2002/n1385.htm" target="_top">The
|
||||
Forwarding Problem</a> for a very detailed discussion including solutions
|
||||
that require language changes.
|
||||
</p>
|
||||
<p>
|
||||
Now, for actually implementing it, we need 2^N overloads for N parameters (each
|
||||
with and without const qualifier) for each number of arguments (that is 2^(Nmax+1)
|
||||
- 2^Nmin). Right, that means the compile-time complexity is O(2^N), however
|
||||
the factor is low so it works quite well for a reasonable number (< 10)
|
||||
of arguments.
|
||||
</p>
|
||||
</div>
|
||||
<div class="section" lang="en">
|
||||
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
|
||||
<a name="boost_functional_forward.reference"></a><a href="index.html#boost_functional_forward.reference" title=" Reference"> Reference</a></h2></div></div></div>
|
||||
<div class="toc"><dl>
|
||||
<dt><span class="section"><a href="index.html#boost_functional_forward.reference.forward_adapter">forward_adapter</a></span></dt>
|
||||
<dt><span class="section"><a href="index.html#boost_functional_forward.reference.lightweight_forward_adapter">lightweight_forward_adapter</a></span></dt>
|
||||
</dl></div>
|
||||
<div class="section" lang="en">
|
||||
<div class="titlepage"><div><div><h3 class="title">
|
||||
<a name="boost_functional_forward.reference.forward_adapter"></a><a href="index.html#boost_functional_forward.reference.forward_adapter" title="forward_adapter">forward_adapter</a></h3></div></div></div>
|
||||
<a name="boost_functional_forward.reference.forward_adapter.description"></a><h4>
|
||||
<a name="id935594"></a>
|
||||
<a href="index.html#boost_functional_forward.reference.forward_adapter.description">Description</a>
|
||||
</h4>
|
||||
<p>
|
||||
Function object adapter template whose instances are callable with LValue
|
||||
and RValue arguments. RValue arguments are forwarded as reference-to-const
|
||||
typed LValues.
|
||||
</p>
|
||||
<p>
|
||||
An arity can be given as second, numeric non-type template argument to restrict
|
||||
forwarding to a specific arity. If a third, numeric non-type template argument
|
||||
is present, the second and third template argument are treated as minimum
|
||||
and maximum arity, respectively. Specifying an arity can be helpful to improve
|
||||
the readability of diagnostic messages and compile time performance.
|
||||
</p>
|
||||
<p>
|
||||
<a href="http://www.boost.org/libs/utility/utility.htm#result_of" target="_top">Boost.ResultOf</a>
|
||||
can be used to determine the result types of specific call expressions.
|
||||
</p>
|
||||
<a name="boost_functional_forward.reference.forward_adapter.header"></a><h4>
|
||||
<a name="id935646"></a>
|
||||
<a href="index.html#boost_functional_forward.reference.forward_adapter.header">Header</a>
|
||||
</h4>
|
||||
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">functional</span><span class="special">/</span><span class="identifier">forward_adapter</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
|
||||
</pre>
|
||||
<a name="boost_functional_forward.reference.forward_adapter.synopsis"></a><h4>
|
||||
<a name="id935721"></a>
|
||||
<a href="index.html#boost_functional_forward.reference.forward_adapter.synopsis">Synopsis</a>
|
||||
</h4>
|
||||
<pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span>
|
||||
<span class="special">{</span>
|
||||
<span class="keyword">template</span><span class="special"><</span> <span class="keyword">class</span> <span class="identifier">Function</span><span class="special">,</span>
|
||||
<span class="keyword">int</span> <span class="identifier">Arity_Or_MinArity</span> <span class="special">=</span> <span class="emphasis"><em>unspecified</em></span><span class="special">,</span> <span class="keyword">int</span> <span class="identifier">MaxArity</span> <span class="special">=</span> <span class="emphasis"><em>unspecified</em></span> <span class="special">></span>
|
||||
<span class="keyword">class</span> <span class="identifier">forward_adapter</span><span class="special">;</span>
|
||||
<span class="special">}</span>
|
||||
</pre>
|
||||
<div class="variablelist">
|
||||
<p class="title"><b>Notation</b></p>
|
||||
<dl>
|
||||
<dt><span class="term"><code class="computeroutput"><span class="identifier">F</span></code></span></dt>
|
||||
<dd><p>
|
||||
a possibly const qualified function object type or reference type thereof
|
||||
</p></dd>
|
||||
<dt><span class="term"><code class="computeroutput"><span class="identifier">f</span></code></span></dt>
|
||||
<dd><p>
|
||||
an object convertible to <code class="computeroutput"><span class="identifier">F</span></code>
|
||||
</p></dd>
|
||||
<dt><span class="term"><code class="computeroutput"><span class="identifier">FA</span></code></span></dt>
|
||||
<dd><p>
|
||||
the type <code class="computeroutput"><span class="identifier">forward_adapter</span><span class="special"><</span><span class="identifier">F</span><span class="special">></span></code>
|
||||
</p></dd>
|
||||
<dt><span class="term"><code class="computeroutput"><span class="identifier">fa</span></code></span></dt>
|
||||
<dd><p>
|
||||
an instance object of <code class="computeroutput"><span class="identifier">FA</span></code>,
|
||||
initialized with <code class="computeroutput"><span class="identifier">f</span></code>
|
||||
</p></dd>
|
||||
<dt><span class="term"><code class="computeroutput"><span class="identifier">a0</span></code>...<code class="computeroutput"><span class="identifier">aN</span></code></span></dt>
|
||||
<dd><p>
|
||||
arguments to <code class="computeroutput"><span class="identifier">fa</span></code>
|
||||
</p></dd>
|
||||
</dl>
|
||||
</div>
|
||||
<p>
|
||||
The result type of a target function invocation must be
|
||||
</p>
|
||||
<pre class="programlisting"><a href="http://www.boost.org/libs/utility/utility.htm#result_of" target="_top"><code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">result_of</span></code></a><span class="special"><</span><span class="identifier">F</span><span class="special">*(</span><span class="identifier">TA0</span> <span class="special">[</span><span class="keyword">const</span><span class="special">]&...</span><span class="identifier">TAN</span> <span class="special">[</span><span class="keyword">const</span><span class="special">]&])>::</span><span class="identifier">type</span>
|
||||
</pre>
|
||||
<p>
|
||||
where <code class="computeroutput"><span class="identifier">TA0</span></code>...<code class="computeroutput"><span class="identifier">TAN</span></code> denote the argument types of <code class="computeroutput"><span class="identifier">a0</span></code>...<code class="computeroutput"><span class="identifier">aN</span></code>.
|
||||
</p>
|
||||
<a name="boost_functional_forward.reference.forward_adapter.expression_semantics"></a><h4>
|
||||
<a name="id936177"></a>
|
||||
<a href="index.html#boost_functional_forward.reference.forward_adapter.expression_semantics">Expression
|
||||
Semantics</a>
|
||||
</h4>
|
||||
<div class="informaltable"><table class="table">
|
||||
<colgroup>
|
||||
<col>
|
||||
<col>
|
||||
</colgroup>
|
||||
<thead><tr>
|
||||
<th>
|
||||
<p>
|
||||
Expression
|
||||
</p>
|
||||
</th>
|
||||
<th>
|
||||
<p>
|
||||
Semantics
|
||||
</p>
|
||||
</th>
|
||||
</tr></thead>
|
||||
<tbody>
|
||||
<tr>
|
||||
<td>
|
||||
<p>
|
||||
<code class="computeroutput"><span class="identifier">FA</span><span class="special">(</span><span class="identifier">f</span><span class="special">)</span></code>
|
||||
</p>
|
||||
</td>
|
||||
<td>
|
||||
<p>
|
||||
creates an adapter, initializes the target function with <code class="computeroutput"><span class="identifier">f</span></code>.
|
||||
</p>
|
||||
</td>
|
||||
</tr>
|
||||
<tr>
|
||||
<td>
|
||||
<p>
|
||||
<code class="computeroutput"><span class="identifier">FA</span><span class="special">()</span></code>
|
||||
</p>
|
||||
</td>
|
||||
<td>
|
||||
<p>
|
||||
creates an adapter, attempts to use <code class="computeroutput"><span class="identifier">F</span></code>'s
|
||||
default constructor.
|
||||
</p>
|
||||
</td>
|
||||
</tr>
|
||||
<tr>
|
||||
<td>
|
||||
<p>
|
||||
<code class="computeroutput"><span class="identifier">fa</span><span class="special">(</span><span class="identifier">a0</span></code>...<code class="computeroutput"><span class="identifier">aN</span><span class="special">)</span></code>
|
||||
</p>
|
||||
</td>
|
||||
<td>
|
||||
<p>
|
||||
calls <code class="computeroutput"><span class="identifier">f</span></code> with with
|
||||
arguments <code class="computeroutput"><span class="identifier">a0</span></code>...<code class="computeroutput"><span class="identifier">aN</span></code>.
|
||||
</p>
|
||||
</td>
|
||||
</tr>
|
||||
</tbody>
|
||||
</table></div>
|
||||
<a name="boost_functional_forward.reference.forward_adapter.limits"></a><h4>
|
||||
<a name="id936405"></a>
|
||||
<a href="index.html#boost_functional_forward.reference.forward_adapter.limits">Limits</a>
|
||||
</h4>
|
||||
<p>
|
||||
The macro BOOST_FUNCTIONAL_FORWARD_ADAPTER_MAX_ARITY can be defined to set
|
||||
the maximum call arity. It defaults to 6.
|
||||
</p>
|
||||
<a name="boost_functional_forward.reference.forward_adapter.complexity"></a><h4>
|
||||
<a name="id936434"></a>
|
||||
<a href="index.html#boost_functional_forward.reference.forward_adapter.complexity">Complexity</a>
|
||||
</h4>
|
||||
<p>
|
||||
Preprocessing time: O(2^N), where N is the arity limit. Compile time: O(2^N),
|
||||
where N depends on the arity range. Run time: O(0) if the compiler inlines,
|
||||
O(1) otherwise.
|
||||
</p>
|
||||
</div>
|
||||
<div class="section" lang="en">
|
||||
<div class="titlepage"><div><div><h3 class="title">
|
||||
<a name="boost_functional_forward.reference.lightweight_forward_adapter"></a><a href="index.html#boost_functional_forward.reference.lightweight_forward_adapter" title="lightweight_forward_adapter">lightweight_forward_adapter</a></h3></div></div></div>
|
||||
<a name="boost_functional_forward.reference.lightweight_forward_adapter.description"></a><h4>
|
||||
<a name="id936485"></a>
|
||||
<a href="index.html#boost_functional_forward.reference.lightweight_forward_adapter.description">Description</a>
|
||||
</h4>
|
||||
<p>
|
||||
Function object adapter template whose instances are callable with LValue
|
||||
and RValue arguments. All arguments are forwarded as reference-to-const typed
|
||||
LValues, except for reference wrappers which are unwrapped and may yield
|
||||
non-const LValues.
|
||||
</p>
|
||||
<p>
|
||||
An arity can be given as second, numeric non-type template argument to restrict
|
||||
forwarding to a specific arity. If a third, numeric non-type template argument
|
||||
is present, the second and third template argument are treated as minimum
|
||||
and maximum arity, respectively. Specifying an arity can be helpful to improve
|
||||
the readability of diagnostic messages and compile time performance.
|
||||
</p>
|
||||
<p>
|
||||
<a href="http://www.boost.org/libs/utility/utility.htm#result_of" target="_top">Boost.ResultOf</a>
|
||||
can be used to determine the result types of specific call expressions.
|
||||
</p>
|
||||
<a name="boost_functional_forward.reference.lightweight_forward_adapter.header"></a><h4>
|
||||
<a name="id936540"></a>
|
||||
<a href="index.html#boost_functional_forward.reference.lightweight_forward_adapter.header">Header</a>
|
||||
</h4>
|
||||
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">functional</span><span class="special">/</span><span class="identifier">lightweight_forward_adapter</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
|
||||
</pre>
|
||||
<a name="boost_functional_forward.reference.lightweight_forward_adapter.synopsis"></a><h4>
|
||||
<a name="id936616"></a>
|
||||
<a href="index.html#boost_functional_forward.reference.lightweight_forward_adapter.synopsis">Synopsis</a>
|
||||
</h4>
|
||||
<pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span>
|
||||
<span class="special">{</span>
|
||||
<span class="keyword">template</span><span class="special"><</span> <span class="keyword">class</span> <span class="identifier">Function</span><span class="special">,</span>
|
||||
<span class="keyword">int</span> <span class="identifier">Arity_Or_MinArity</span> <span class="special">=</span> <span class="emphasis"><em>unspecified</em></span><span class="special">,</span> <span class="keyword">int</span> <span class="identifier">MaxArity</span> <span class="special">=</span> <span class="emphasis"><em>unspecified</em></span> <span class="special">></span>
|
||||
<span class="keyword">struct</span> <span class="identifier">lightweight_forward_adapter</span><span class="special">;</span>
|
||||
<span class="special">}</span>
|
||||
</pre>
|
||||
<div class="variablelist">
|
||||
<p class="title"><b>Notation</b></p>
|
||||
<dl>
|
||||
<dt><span class="term"><code class="computeroutput"><span class="identifier">F</span></code></span></dt>
|
||||
<dd><p>
|
||||
a possibly const qualified function object type or reference type thereof
|
||||
</p></dd>
|
||||
<dt><span class="term"><code class="computeroutput"><span class="identifier">f</span></code></span></dt>
|
||||
<dd><p>
|
||||
an object convertible to <code class="computeroutput"><span class="identifier">F</span></code>
|
||||
</p></dd>
|
||||
<dt><span class="term"><code class="computeroutput"><span class="identifier">FA</span></code></span></dt>
|
||||
<dd><p>
|
||||
the type <code class="computeroutput"><span class="identifier">lightweight_forward_adapter</span><span class="special"><</span><span class="identifier">F</span><span class="special">></span></code>
|
||||
</p></dd>
|
||||
<dt><span class="term"><code class="computeroutput"><span class="identifier">fa</span></code></span></dt>
|
||||
<dd><p>
|
||||
an instance of <code class="computeroutput"><span class="identifier">FA</span></code>, initialized
|
||||
with <code class="computeroutput"><span class="identifier">f</span></code>
|
||||
</p></dd>
|
||||
<dt><span class="term"><code class="computeroutput"><span class="identifier">a0</span></code>...<code class="computeroutput"><span class="identifier">aN</span></code></span></dt>
|
||||
<dd><p>
|
||||
arguments to <code class="computeroutput"><span class="identifier">fa</span></code>
|
||||
</p></dd>
|
||||
</dl>
|
||||
</div>
|
||||
<p>
|
||||
The result type of a target function invocation must be
|
||||
</p>
|
||||
<pre class="programlisting"><a href="http://www.boost.org/libs/utility/utility.htm#result_of" target="_top"><code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">result_of</span></code></a><span class="special"><</span><span class="identifier">F</span><span class="special">*(</span><span class="identifier">TA0</span> <span class="special">[</span><span class="keyword">const</span><span class="special">]&...</span><span class="identifier">TAN</span> <span class="special">[</span><span class="keyword">const</span><span class="special">]&])>::</span><span class="identifier">type</span>
|
||||
</pre>
|
||||
<p>
|
||||
where <code class="computeroutput"><span class="identifier">TA0</span></code>...<code class="computeroutput"><span class="identifier">TAN</span></code> denote the argument types of <code class="computeroutput"><span class="identifier">a0</span></code>...<code class="computeroutput"><span class="identifier">aN</span></code>.
|
||||
</p>
|
||||
<a name="boost_functional_forward.reference.lightweight_forward_adapter.expression_semantics"></a><h4>
|
||||
<a name="id937073"></a>
|
||||
<a href="index.html#boost_functional_forward.reference.lightweight_forward_adapter.expression_semantics">Expression
|
||||
Semantics</a>
|
||||
</h4>
|
||||
<div class="informaltable"><table class="table">
|
||||
<colgroup>
|
||||
<col>
|
||||
<col>
|
||||
</colgroup>
|
||||
<thead><tr>
|
||||
<th>
|
||||
<p>
|
||||
Expression
|
||||
</p>
|
||||
</th>
|
||||
<th>
|
||||
<p>
|
||||
Semantics
|
||||
</p>
|
||||
</th>
|
||||
</tr></thead>
|
||||
<tbody>
|
||||
<tr>
|
||||
<td>
|
||||
<p>
|
||||
<code class="computeroutput"><span class="identifier">FA</span><span class="special">(</span><span class="identifier">f</span><span class="special">)</span></code>
|
||||
</p>
|
||||
</td>
|
||||
<td>
|
||||
<p>
|
||||
creates an adapter, initializes the target function with <code class="computeroutput"><span class="identifier">f</span></code>.
|
||||
</p>
|
||||
</td>
|
||||
</tr>
|
||||
<tr>
|
||||
<td>
|
||||
<p>
|
||||
<code class="computeroutput"><span class="identifier">FA</span><span class="special">()</span></code>
|
||||
</p>
|
||||
</td>
|
||||
<td>
|
||||
<p>
|
||||
creates an adapter, attempts to use <code class="computeroutput"><span class="identifier">F</span></code>'s
|
||||
default constructor.
|
||||
</p>
|
||||
</td>
|
||||
</tr>
|
||||
<tr>
|
||||
<td>
|
||||
<p>
|
||||
<code class="computeroutput"><span class="identifier">fa</span><span class="special">(</span><span class="identifier">a0</span></code>...<code class="computeroutput"><span class="identifier">aN</span><span class="special">)</span></code>
|
||||
</p>
|
||||
</td>
|
||||
<td>
|
||||
<p>
|
||||
calls <code class="computeroutput"><span class="identifier">f</span></code> with with
|
||||
const arguments <code class="computeroutput"><span class="identifier">a0</span></code>...<code class="computeroutput"><span class="identifier">aN</span></code>. If <code class="computeroutput"><span class="identifier">aI</span></code>
|
||||
is a reference wrapper it is unwrapped.
|
||||
</p>
|
||||
</td>
|
||||
</tr>
|
||||
</tbody>
|
||||
</table></div>
|
||||
<a name="boost_functional_forward.reference.lightweight_forward_adapter.limits"></a><h4>
|
||||
<a name="id937311"></a>
|
||||
<a href="index.html#boost_functional_forward.reference.lightweight_forward_adapter.limits">Limits</a>
|
||||
</h4>
|
||||
<p>
|
||||
The macro BOOST_FUNCTIONAL_LIGHTWEIGHT_FORWARD_ADAPTER_MAX_ARITY can be defined
|
||||
to set the maximum call arity. It defaults to 10.
|
||||
</p>
|
||||
<a name="boost_functional_forward.reference.lightweight_forward_adapter.complexity"></a><h4>
|
||||
<a name="id937342"></a>
|
||||
<a href="index.html#boost_functional_forward.reference.lightweight_forward_adapter.complexity">Complexity</a>
|
||||
</h4>
|
||||
<p>
|
||||
Preprocessing time: O(N), where N is the arity limit. Compile time: O(N),
|
||||
where N is the effective arity of a call. Run time: O(0) if the compiler
|
||||
inlines, O(1) otherwise.
|
||||
</p>
|
||||
</div>
|
||||
</div>
|
||||
<div class="section" lang="en">
|
||||
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
|
||||
<a name="boost_functional_forward.acknowledgements"></a><a href="index.html#boost_functional_forward.acknowledgements" title="Acknowledgements">Acknowledgements</a></h2></div></div></div>
|
||||
<p>
|
||||
As these utilities are factored out of the <a href="http://www.boost.org/libs/fusion/doc/html/index.html" target="_top">Boost.Fusion</a>
|
||||
functional module, I want to thank Dan Marsden and Joel de Guzman for letting
|
||||
me participate in the development of that great library in the first place.
|
||||
</p>
|
||||
<p>
|
||||
Further, I want to credit the authors of the references below, for their in-depth
|
||||
investigation of the problem and the solution implemented here.
|
||||
</p>
|
||||
<p>
|
||||
Last but not least I want to thank Vesa Karnoven and Paul Mensonides for the
|
||||
Boost Preprocessor library. Without it, I would have ended up with an external
|
||||
code generator for this one.
|
||||
</p>
|
||||
</div>
|
||||
<div class="section" lang="en">
|
||||
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
|
||||
<a name="boost_functional_forward.references"></a><a href="index.html#boost_functional_forward.references" title="References">References</a></h2></div></div></div>
|
||||
<div class="orderedlist"><ol type="1">
|
||||
<li>
|
||||
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2002/n1385.htm" target="_top">The
|
||||
Forwarding Problem</a>, Peter Dimov, Howard E. Hinnant, David Abrahams,
|
||||
2002
|
||||
</li>
|
||||
<li>
|
||||
<a href="http://www.boost.org/libs/utility/utility.htm#result_of" target="_top">Boost.ResultOf</a>,
|
||||
Douglas Gregor, 2004
|
||||
</li>
|
||||
<li>
|
||||
<a href="http://www.boost.org/doc/html/ref.html" target="_top">Boost.Ref</a>, Jaakko
|
||||
Jarvi, Peter Dimov, Douglas Gregor, David Abrahams, 1999-2002
|
||||
</li>
|
||||
</ol></div>
|
||||
</div>
|
||||
</div>
|
||||
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
|
||||
<td align="left"><p><small>Last revised: November 01, 2008 at 19:58:50 GMT</small></p></td>
|
||||
<td align="right"><div class="copyright-footer"></div></td>
|
||||
</tr></table>
|
||||
<hr>
|
||||
<div class="spirit-nav"></div>
|
||||
</body>
|
||||
</html>
|
||||
20
forward/test/Jamfile
Normal file
20
forward/test/Jamfile
Normal file
@@ -0,0 +1,20 @@
|
||||
|
||||
# (C) Copyright Tobias Schwinger
|
||||
#
|
||||
# Use modification and distribution are subject to the boost Software License,
|
||||
# Version 1.0. (See http:/\/www.boost.org/LICENSE_1_0.txt).
|
||||
|
||||
import testing ;
|
||||
|
||||
project forward-tests
|
||||
: requirements
|
||||
<include>/Users/tosh/Lab/boost
|
||||
<include>/Users/tosh/Lab/deploy/x_files/forward
|
||||
;
|
||||
|
||||
test-suite functional/forward
|
||||
:
|
||||
[ run forward_adapter.cpp ]
|
||||
[ run lightweight_forward_adapter.cpp ]
|
||||
;
|
||||
|
||||
127
forward/test/forward_adapter.cpp
Normal file
127
forward/test/forward_adapter.cpp
Normal file
@@ -0,0 +1,127 @@
|
||||
/*=============================================================================
|
||||
Copyright (c) 2007 Tobias Schwinger
|
||||
|
||||
Use modification and distribution are subject to the Boost Software
|
||||
License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
|
||||
http://www.boost.org/LICENSE_1_0.txt).
|
||||
==============================================================================*/
|
||||
|
||||
#include <boost/config.hpp>
|
||||
|
||||
#ifdef BOOST_MSVC
|
||||
# pragma warning(disable: 4244) // no conversion warnings, please
|
||||
#endif
|
||||
|
||||
#include <boost/detail/lightweight_test.hpp>
|
||||
#include <boost/functional/forward_adapter.hpp>
|
||||
|
||||
#include <boost/type_traits/is_same.hpp>
|
||||
|
||||
#include <boost/blank.hpp>
|
||||
#include <boost/noncopyable.hpp>
|
||||
|
||||
#include <memory>
|
||||
|
||||
template <class Base = boost::blank>
|
||||
class test_func : public Base
|
||||
{
|
||||
int val;
|
||||
public:
|
||||
test_func(int v) : val(v) { }
|
||||
|
||||
template<class B>
|
||||
test_func(test_func<B> const & that)
|
||||
: val(that.val)
|
||||
{ }
|
||||
|
||||
template<class B> friend class test_func;
|
||||
|
||||
int operator()(int & l, int const & r) const
|
||||
{
|
||||
return l=r+val;
|
||||
}
|
||||
long operator()(int & l, int const & r)
|
||||
{
|
||||
return -(l=r+val);
|
||||
}
|
||||
|
||||
template <typename Sig>
|
||||
struct result
|
||||
{
|
||||
typedef void type;
|
||||
};
|
||||
|
||||
// ensure result_of argument types are what's expected
|
||||
// note: this is *not* how client code should look like
|
||||
template <class Self>
|
||||
struct result< Self const(int&,int const&) > { typedef int type; };
|
||||
|
||||
template <class Self>
|
||||
struct result< Self(int&,int const&) > { typedef long type; };
|
||||
|
||||
template <class Self>
|
||||
struct result< Self(int&,int&) > { typedef char type; };
|
||||
};
|
||||
|
||||
enum { int_, long_, char_ };
|
||||
|
||||
int type_of(int) { return int_; }
|
||||
int type_of(long) { return long_; }
|
||||
int type_of(char) { return char_; }
|
||||
|
||||
int main()
|
||||
{
|
||||
{
|
||||
using boost::is_same;
|
||||
using boost::result_of;
|
||||
typedef boost::forward_adapter< test_func<> > f;
|
||||
|
||||
// lvalue,rvalue
|
||||
BOOST_TEST(( is_same<
|
||||
result_of< f(int&, int) >::type, long >::value ));
|
||||
BOOST_TEST(( is_same<
|
||||
result_of< f const (int&, int) >::type, int >::value ));
|
||||
// lvalue,const lvalue
|
||||
BOOST_TEST(( is_same<
|
||||
result_of< f(int&, int const &) >::type, long >::value ));
|
||||
BOOST_TEST(( is_same<
|
||||
result_of< f const (int&, int const &) >::type, int >::value ));
|
||||
// lvalue,lvalue
|
||||
BOOST_TEST(( is_same<
|
||||
result_of< f(int&, int&) >::type, char >::value ));
|
||||
BOOST_TEST(( is_same<
|
||||
result_of< f const (int&, int&) >::type, char >::value ));
|
||||
}
|
||||
{
|
||||
using boost::noncopyable;
|
||||
using boost::forward_adapter;
|
||||
|
||||
int x = 0;
|
||||
test_func<noncopyable> f(7);
|
||||
forward_adapter< test_func<> > func(f);
|
||||
forward_adapter< test_func<noncopyable> & > func_ref(f);
|
||||
forward_adapter< test_func<noncopyable> & > const func_ref_c(f);
|
||||
forward_adapter< test_func<> const > func_c(f);
|
||||
forward_adapter< test_func<> > const func_c2(f);
|
||||
forward_adapter< test_func<noncopyable> const & > func_c_ref(f);
|
||||
|
||||
BOOST_TEST( type_of( func(x,1) ) == long_ );
|
||||
BOOST_TEST( type_of( func_ref(x,1) ) == long_ );
|
||||
BOOST_TEST( type_of( func_ref_c(x,1) ) == long_ );
|
||||
BOOST_TEST( type_of( func_c(x,1) ) == int_ );
|
||||
BOOST_TEST( type_of( func_c2(x,1) ) == int_ );
|
||||
BOOST_TEST( type_of( func_c_ref(x,1) ) == int_ );
|
||||
BOOST_TEST( type_of( func(x,x) ) == char_ );
|
||||
|
||||
BOOST_TEST( func(x,1) == -8 );
|
||||
BOOST_TEST( func_ref(x,1) == -8 );
|
||||
BOOST_TEST( func_ref_c(x,1) == -8 );
|
||||
BOOST_TEST( func_c(x,1) == 8 );
|
||||
BOOST_TEST( func_c2(x,1) == 8 );
|
||||
BOOST_TEST( func_c_ref(x,1) == 8 );
|
||||
}
|
||||
|
||||
return boost::report_errors();
|
||||
}
|
||||
|
||||
|
||||
128
forward/test/lightweight_forward_adapter.cpp
Normal file
128
forward/test/lightweight_forward_adapter.cpp
Normal file
@@ -0,0 +1,128 @@
|
||||
/*=============================================================================
|
||||
Copyright (c) 2007 Tobias Schwinger
|
||||
|
||||
Use modification and distribution are subject to the Boost Software
|
||||
License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
|
||||
http://www.boost.org/LICENSE_1_0.txt).
|
||||
==============================================================================*/
|
||||
|
||||
#include <boost/config.hpp>
|
||||
|
||||
#ifdef BOOST_MSVC
|
||||
# pragma warning(disable: 4244) // no conversion warnings, please
|
||||
#endif
|
||||
|
||||
#include <boost/detail/lightweight_test.hpp>
|
||||
#include <boost/functional/lightweight_forward_adapter.hpp>
|
||||
|
||||
#include <boost/type_traits/is_same.hpp>
|
||||
|
||||
#include <boost/blank.hpp>
|
||||
#include <boost/noncopyable.hpp>
|
||||
|
||||
#include <memory>
|
||||
|
||||
template <class Base = boost::blank>
|
||||
class test_func : public Base
|
||||
{
|
||||
int val;
|
||||
public:
|
||||
test_func(int v) : val(v) { }
|
||||
|
||||
template<class B>
|
||||
test_func(test_func<B> const & that)
|
||||
: val(that.val)
|
||||
{ }
|
||||
|
||||
template<class B> friend class test_func;
|
||||
|
||||
int operator()(int & l, int const & r) const
|
||||
{
|
||||
return l=r+val;
|
||||
}
|
||||
long operator()(int & l, int const & r)
|
||||
{
|
||||
return -(l=r+val);
|
||||
}
|
||||
|
||||
template <typename Sig>
|
||||
struct result
|
||||
{
|
||||
typedef void type;
|
||||
};
|
||||
|
||||
// ensure result_of argument types are what's expected
|
||||
// note: this is *not* how client code should look like
|
||||
template <class Self>
|
||||
struct result< Self const(int&,int const&) > { typedef int type; };
|
||||
|
||||
template <class Self>
|
||||
struct result< Self(int&,int const&) > { typedef long type; };
|
||||
|
||||
template <class Self>
|
||||
struct result< Self(int&,int&) > { typedef char type; };
|
||||
};
|
||||
|
||||
enum { int_, long_, char_ };
|
||||
|
||||
int type_of(int) { return int_; }
|
||||
int type_of(long) { return long_; }
|
||||
int type_of(char) { return char_; }
|
||||
|
||||
int main()
|
||||
{
|
||||
{
|
||||
using boost::is_same;
|
||||
using boost::result_of;
|
||||
typedef boost::lightweight_forward_adapter< test_func<> > f;
|
||||
typedef boost::reference_wrapper<int> ref;
|
||||
typedef boost::reference_wrapper<int const> cref;
|
||||
|
||||
// lvalue,rvalue
|
||||
BOOST_TEST(( is_same<
|
||||
result_of< f(ref, int) >::type, long >::value ));
|
||||
BOOST_TEST(( is_same<
|
||||
result_of< f const (ref, int) >::type, int >::value ));
|
||||
// lvalue,const lvalue
|
||||
BOOST_TEST(( is_same<
|
||||
result_of< f(ref, cref) >::type, long >::value ));
|
||||
BOOST_TEST(( is_same<
|
||||
result_of< f const (ref, cref) >::type, int >::value ));
|
||||
// lvalue,lvalue
|
||||
BOOST_TEST(( is_same<
|
||||
result_of< f(ref, ref) >::type, char >::value ));
|
||||
BOOST_TEST(( is_same<
|
||||
result_of< f const (ref, ref) >::type, char >::value ));
|
||||
}
|
||||
{
|
||||
using boost::noncopyable;
|
||||
using boost::lightweight_forward_adapter;
|
||||
|
||||
int v = 0; boost::reference_wrapper<int> x(v);
|
||||
test_func<noncopyable> f(7);
|
||||
lightweight_forward_adapter< test_func<> > func(f);
|
||||
lightweight_forward_adapter< test_func<noncopyable> & > func_ref(f);
|
||||
lightweight_forward_adapter< test_func<noncopyable> & > const func_ref_c(f);
|
||||
lightweight_forward_adapter< test_func<> const > func_c(f);
|
||||
lightweight_forward_adapter< test_func<> > const func_c2(f);
|
||||
lightweight_forward_adapter< test_func<noncopyable> const & > func_c_ref(f);
|
||||
|
||||
BOOST_TEST( type_of( func(x,1) ) == long_ );
|
||||
BOOST_TEST( type_of( func_ref(x,1) ) == long_ );
|
||||
BOOST_TEST( type_of( func_ref_c(x,1) ) == long_ );
|
||||
BOOST_TEST( type_of( func_c(x,1) ) == int_ );
|
||||
BOOST_TEST( type_of( func_c2(x,1) ) == int_ );
|
||||
BOOST_TEST( type_of( func_c_ref(x,1) ) == int_ );
|
||||
BOOST_TEST( type_of( func(x,x) ) == char_ );
|
||||
|
||||
BOOST_TEST( func(x,1) == -8 );
|
||||
BOOST_TEST( func_ref(x,1) == -8 );
|
||||
BOOST_TEST( func_ref_c(x,1) == -8 );
|
||||
BOOST_TEST( func_c(x,1) == 8 );
|
||||
BOOST_TEST( func_c2(x,1) == 8 );
|
||||
BOOST_TEST( func_c_ref(x,1) == 8 );
|
||||
}
|
||||
|
||||
return boost::report_errors();
|
||||
}
|
||||
|
||||
Reference in New Issue
Block a user