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Full merge from trunk at revision 41356 of entire boost-root tree.

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[SVN r41369]
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Beman Dawes
2007-11-25 18:07:19 +00:00
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237
example/cookbook/do_the_bind.cpp
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/*=============================================================================
Copyright (c) 2006-2007 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).
Problem:
How to "do the Bind?"
This recipe shows how to implement a function binder, similar to
Boost.Bind based on the Functional module of Fusion.
It works as follows:
'bind' is a global, stateless function object. It is implemented in
fused form (fused_binder) and transformed into a variadic function
object. When called, 'bind' returns another function object, which
holds the arguments of the call to 'bind'. It is, again, implemented
in fused form (fused_bound_function) and transformed into unfused
form.
==============================================================================*/
#include <boost/fusion/functional/invocation/invoke.hpp>
#include <boost/fusion/functional/adapter/unfused_generic.hpp>
#include <boost/fusion/functional/adapter/unfused_rvalue_args.hpp>
#include <boost/fusion/support/deduce_sequence.hpp>
#include <boost/fusion/sequence/intrinsic/at.hpp>
#include <boost/fusion/mpl.hpp>
#include <boost/fusion/sequence/intrinsic/front.hpp>
#include <boost/fusion/sequence/intrinsic/empty.hpp>
#include <boost/fusion/algorithm/transformation/transform.hpp>
#include <boost/fusion/algorithm/transformation/pop_front.hpp>
#include <boost/type_traits/remove_reference.hpp>
#include <boost/mpl/eval_if.hpp>
#include <boost/mpl/identity.hpp>
#include <boost/mpl/int.hpp>
#include <boost/ref.hpp>
#include <iostream>
#include <typeinfo>
namespace impl
{
namespace fusion = boost::fusion;
namespace traits = boost::fusion::traits;
namespace result_of = boost::fusion::result_of;
namespace mpl = boost::mpl;
using mpl::placeholders::_;
// Placeholders (we inherit from mpl::int_, so we can use placeholders
// as indices for fusion::at, later)
template <int I> struct placeholder : mpl::int_<I> { };
// A traits class to find out whether T is a placeholeder
template <typename T> struct is_placeholder : mpl::false_ { };
template <int I> struct is_placeholder< placeholder<I> > : mpl::true_ { };
template <int I> struct is_placeholder< placeholder<I> & > : mpl::true_ { };
template <int I> struct is_placeholder< placeholder<I> const > : mpl::true_ { };
template <int I> struct is_placeholder< placeholder<I> const & > : mpl::true_ { };
// This class template provides a Polymorphic Function Object to be used
// with fusion::transform. It is applied to the sequence of arguments that
// describes the binding and holds a reference to the sequence of arguments
// from the final call.
template<class FinalArgs> struct argument_transform
{
FinalArgs const & ref_final_args;
public:
explicit argument_transform(FinalArgs const & final_args)
: ref_final_args(final_args)
{ }
// A placeholder? Replace it with an argument from the final call...
template <int Index>
inline typename result_of::at_c<FinalArgs const, Index>::type
operator()(placeholder<Index> const &) const
{
return fusion::at_c<Index>(this->ref_final_args);
}
// ...just return the bound argument, otherwise.
template <typename T> inline T & operator()(T & bound) const
{
return bound;
}
template <typename Signature>
struct result;
template <class Self, typename T>
struct result< Self (T) >
: mpl::eval_if< is_placeholder<T>,
result_of::at<FinalArgs,typename boost::remove_reference<T>::type>,
mpl::identity<T>
>
{ };
};
// Fused implementation of the bound function, the function object
// returned by bind
template <class BindArgs> class fused_bound_function
{
typedef typename traits::deduce_sequence<BindArgs>::type bound_args;
bound_args fsq_bind_args;
public:
fused_bound_function(BindArgs const & bind_args)
: fsq_bind_args(bind_args)
{ }
template <typename Signature>
struct result;
template <class FinalArgs>
struct result_impl
: result_of::invoke< typename result_of::front<bound_args>::type,
typename result_of::transform<
typename result_of::pop_front<bound_args>::type,
argument_transform<FinalArgs> const
>::type
>
{ };
template <class Self, class FinalArgs>
struct result< Self (FinalArgs) >
: result_impl< typename boost::remove_reference<FinalArgs>::type >
{ };
template <class FinalArgs>
inline typename result_impl<FinalArgs>::type
operator()(FinalArgs const & final_args) const
{
return fusion::invoke( fusion::front(this->fsq_bind_args),
fusion::transform( fusion::pop_front(this->fsq_bind_args),
argument_transform<FinalArgs>(final_args) ) );
}
// Could add a non-const variant - omitted for readability
};
// Fused implementation of the 'bind' function
struct fused_binder
{
template <class Signature>
struct result;
template <class BindArgs>
struct result_impl
{
// We have to transform the arguments so they are held by-value
// in the returned function.
typedef fusion::unfused_generic<
fused_bound_function<BindArgs> > type;
};
template <class Self, class BindArgs>
struct result< Self (BindArgs) >
: result_impl< typename boost::remove_reference<BindArgs>::type >
{ };
template <class BindArgs>
inline typename result_impl< BindArgs >::type
operator()(BindArgs & bind_args) const
{
return typename result< void(BindArgs) >::type(bind_args);
}
};
// The binder's unfused type. We use unfused_rvalue_args to make that
// thing more similar to Boost.Bind. Because of that we have to use
// Boost.Ref (below in the sample code)
typedef fusion::unfused_rvalue_args<fused_binder> binder;
}
// Placeholder globals
impl::placeholder<0> const _1_ = impl::placeholder<0>();
impl::placeholder<1> const _2_ = impl::placeholder<1>();
impl::placeholder<2> const _3_ = impl::placeholder<2>();
impl::placeholder<3> const _4_ = impl::placeholder<3>();
// The bind function is a global, too
impl::binder const bind = impl::binder();
// OK, let's try it out:
struct func
{
typedef int result_type;
inline int operator()() const
{
std::cout << "operator()" << std::endl;
return 0;
}
template <typename A>
inline int operator()(A const & a) const
{
std::cout << "operator()(A const & a)" << std::endl;
std::cout << " a = " << a << " A = " << typeid(A).name() << std::endl;
return 1;
}
template <typename A, typename B>
inline int operator()(A const & a, B & b) const
{
std::cout << "operator()(A const & a, B & b)" << std::endl;
std::cout << " a = " << a << " A = " << typeid(A).name() << std::endl;
std::cout << " b = " << b << " B = " << typeid(B).name() << std::endl;
return 2;
}
};
int main()
{
func f;
int value = 42;
using boost::ref;
int errors = 0;
errors += !( bind(f)() == 0);
errors += !( bind(f,"Hi")() == 1);
errors += !( bind(f,_1_)("there.") == 1);
errors += !( bind(f,"The answer is",_1_)(value) == 2);
errors += !( bind(f,_1_,ref(value))("Really?") == 2);
errors += !( bind(f,_1_,_2_)("Dunno. If there is an answer, it's",value) == 2);
return !! errors;
}

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example/cookbook/fill_em_up.cpp
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/*=============================================================================
Copyright (c) 2006 Joel de Guzman
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)
Problem:
So... you have an input sequence I and a target vector R. You want to
copy I into R. But, I may have less elements than the result vector R.
For those elements not in R, you want them to be default constructed.
Here's a case:
I: list<double, std::string>
R: vector<double, std::string, int, short>
You want the elements at the right of I not in R (i.e. int, short)
default constructed. Those at the left, found in both I and R, you want
to simply copy from I.
Of course you want to be able to handle any type of I and R.
==============================================================================*/
// We'll use these containers as examples
#include <boost/fusion/container/list.hpp>
#include <boost/fusion/container/vector.hpp>
// For doing I/O
#include <boost/fusion/sequence/io.hpp>
// We'll use join and advance for processing
#include <boost/fusion/algorithm/transformation/join.hpp>
#include <boost/fusion/iterator/advance.hpp>
// The fusion <--> MPL link header
#include <boost/fusion/mpl.hpp>
// Same-o same-o
#include <iostream>
#include <string>
int
main()
{
using namespace boost::fusion;
using namespace boost;
// Let's specify our own tuple delimeters for nicer printing
std::cout << tuple_open('[');
std::cout << tuple_close(']');
std::cout << tuple_delimiter(", ");
// Here's your input sequence
typedef list<double, std::string> I;
I i(123.456, "Hello");
// Here's your output sequence. For now, it is just a typedef
typedef vector<double, std::string, int, short> R;
// Let's get the sizes of the sequences. Yeah, you already know that.
// But with templates, you are simply given, say, R and I, corresponding
// to the types of the sequences. You'll have to deal with it generically.
static int const r_size = result_of::size<R>::value;
static int const i_size = result_of::size<I>::value;
// Make sure that I has no more elements than R
// Be nice and catch obvious errors earlier rather than later.
// Without this assert, the mistake will still be caught by Fusion,
// but the error will point to somewhere really obscure.
BOOST_STATIC_ASSERT(i_size <= r_size);
// Let's get the begin and end iterator types of the output sequence
// There's no actual vector yet. We just want to know the types.
typedef result_of::begin<R>::type r_begin;
typedef result_of::end<R>::type r_end;
// Let's skip i_size elements from r_begin. Again, we just want to know the type.
typedef result_of::advance_c<r_begin, i_size>::type r_advance;
// Now, make MPL iterators from r_advance and r_end. Ditto, just types.
typedef mpl::fusion_iterator<r_advance> mpl_r_advance;
typedef mpl::fusion_iterator<r_end> mpl_r_end;
// Make an mpl::iterator_range from the MPL iterators we just created
// You guessed it! --just a type.
typedef mpl::iterator_range<mpl_r_advance, mpl_r_end> tail;
// Use join to join the input sequence and our mpl::iterator_range
// Our mpl::iterator_range is 'tail'. Here, we'll actually instantiate
// 'tail'. Notice that this is a flyweight object, typically just 1 byte
// in size -- it doesn't really hold any data, but is a fully conforming
// sequence nonetheless. When asked to return its elements, 'tail' returns
// each element default constructed. Breeds like a rabbit!
// Construct R from the joined sequences:
R r(join(i, tail()));
// Then finally, print the result:
std::cout << r << std::endl;
return 0;
}