forked from boostorg/typeof
removed tabs
[SVN r31198]
This commit is contained in:
Arkadiy Vertleyb
@ -4,7 +4,7 @@
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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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<ulink url="http://www.boost.org/LICENSE_1_0.txt">
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<ulink url="http://www.boost.org/LICENSE_1_0.txt">
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http://www.boost.org/LICENSE_1_0.txt
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</ulink>)
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]
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@ -22,21 +22,21 @@ by utilizing the C++ template argument deduction facility. Consider `std::pair`
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In order to instantiate this class template and create a temporary object of this instantiation,
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one has to supply both type parameters and value parameters:
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std::pair<int, double>(5, 3.14159);
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std::pair<int, double>(5, 3.14159);
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To avoid this duplication, STL supplies the `std::make_pair` object generator.
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When it is used, the types of template parameters are deduced from supplied function arguments:
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std::make_pair(5, 3.14159);
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std::make_pair(5, 3.14159);
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For the temporary objects it is enough. However, when a named object needs to be allocated,
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the problem appears again:
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std::pair<int, double> p(5, 3.14159);
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std::pair<int, double> p(5, 3.14159);
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The object generator no longer helps:
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std::pair<int, double> p = std::make_pair(5, 3.14159);
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std::pair<int, double> p = std::make_pair(5, 3.14159);
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It would be nice to deduce the type of the object (on the left) from the expression
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it is initialized with (on the right), but the current C++ syntax does not allow for this.
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@ -45,37 +45,37 @@ The above example demonstrates the essence of the problem but does not demonstra
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Many libraries, especially expression template libraries, create objects of really complicated types,
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and go a long way to hide this complexity behind object generators. Consider a nit Boost.Lambda functor:
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_1 > 15 && _2 < 20
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_1 > 15 && _2 < 20
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If one wanted to allocate a named copy of such an innocently looking functor,
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she would have to specify something like this:
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lambda_functor<
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lambda_functor_base<
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logical_action<and_action>,
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tuple<
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lambda_functor<
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lambda_functor_base<
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relational_action<greater_action>,
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tuple<
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lambda_functor<placeholder<1> >,
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int const
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>
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>
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>,
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lambda_functor<
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lambda_functor_base<
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relational_action<less_action>,
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tuple<
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lambda_functor<placeholder<2> >,
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int const
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>
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>
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>
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>
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>
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>
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f = _1 > 15 && _2 < 20;
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lambda_functor<
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lambda_functor_base<
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logical_action<and_action>,
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tuple<
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lambda_functor<
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lambda_functor_base<
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relational_action<greater_action>,
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tuple<
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lambda_functor<placeholder<1> >,
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int const
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>
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>
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>,
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lambda_functor<
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lambda_functor_base<
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relational_action<less_action>,
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tuple<
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lambda_functor<placeholder<2> >,
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int const
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>
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>
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>
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>
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>
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>
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f = _1 > 15 && _2 < 20;
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Not exactly elegant. To solve this problem, the C++ standard committee is considering
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@ -87,11 +87,11 @@ The `typeof` operator (or `decltype`, which is a slightly different flavor of `t
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allows one to determine the type of an expression at compile time. Using `typeof`,
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the above example can be simplified drastically:
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typeof(_1 > 15 && _2 < 20) f = _1 > 15 && _2 < 20;
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typeof(_1 > 15 && _2 < 20) f = _1 > 15 && _2 < 20;
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Much better, but some duplication still exists. The `auto` type solves the rest of the problem:
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auto f = _1 > 15 && _2 < 20;
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auto f = _1 > 15 && _2 < 20;
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[endsect]
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@ -774,11 +774,11 @@ We get the following error message from VC7.1
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[pre
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error C2504: 'boost::type_of::'anonymous-namespace'::encode_type_impl<V,Type_Not_Registered_With_Typeof_System>' : base
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class undefined
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with
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\[
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V=boost::type_of::'anonymous-namespace'::encode_type_impl<boost::mpl::vector0<boost::mpl::na>,std::pair<X,Y<int,true>>>::V0,
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Type_Not_Registered_With_Typeof_System=X
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\]
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with
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\[
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V=boost::type_of::'anonymous-namespace'::encode_type_impl<boost::mpl::vector0<boost::mpl::na>,std::pair<X,Y<int,true>>>::V0,
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Type_Not_Registered_With_Typeof_System=X
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\]
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]
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Inspecting this error message, we see that the compiler complains about `X`
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@ -790,11 +790,11 @@ Recompiling, we get a new error message from VC7.1
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[pre
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error C2504: 'boost::type_of::'anonymous-namespace'::encode_type_impl<V,Type_Not_Registered_With_Typeof_System>' : base
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class undefined
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with
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\[
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V=boost::type_of::'anonymous-namespace'::encode_type_impl<boost::mpl::vector0<boost::mpl::na>,std::pair<X,Y<int,true>>>::V1,
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Type_Not_Registered_With_Typeof_System=Y<int,true>
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\]
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with
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\[
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V=boost::type_of::'anonymous-namespace'::encode_type_impl<boost::mpl::vector0<boost::mpl::na>,std::pair<X,Y<int,true>>>::V1,
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Type_Not_Registered_With_Typeof_System=Y<int,true>
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\]
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]
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Inspecting this error message, we see that the compiler complains about `Y<int,true>`.
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@ -841,8 +841,8 @@ as nested classes. Instead, instantiations can be registered:
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[section:cont Contributed By:]
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* Compliant compilers -- Arkadiy Vertleyb, Peder Holt
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* MSVC 6.5, 7.0, 7.1 -- Igor Chesnokov, Peder Holt
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* Compliant compilers -- Arkadiy Vertleyb, Peder Holt
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* MSVC 6.5, 7.0, 7.1 -- Igor Chesnokov, Peder Holt
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[endsect]
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