boost/type_erasure/param.hpp
// Boost.TypeErasure library
//
// Copyright 2011 Steven Watanabe
//
// 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)
//
// $Id$
#ifndef BOOST_TYPE_ERASURE_PARAM_HPP_INCLUDED
#define BOOST_TYPE_ERASURE_PARAM_HPP_INCLUDED
#include <boost/config.hpp>
#include <boost/utility/enable_if.hpp>
#include <boost/type_traits/is_same.hpp>
#include <boost/type_traits/add_const.hpp>
#include <boost/type_traits/remove_cv.hpp>
#include <boost/type_traits/remove_reference.hpp>
#include <boost/mpl/bool.hpp>
#include <boost/mpl/if.hpp>
#include <boost/type_erasure/detail/access.hpp>
#include <boost/type_erasure/detail/storage.hpp>
#include <boost/type_erasure/is_placeholder.hpp>
#include <boost/type_erasure/concept_of.hpp>
namespace boost {
namespace type_erasure {
template<class Concept, class T>
class any;
template<class Concept>
class binding;
namespace detail {
struct access;
}
namespace detail {
template<class From, class To>
struct placeholder_conversion : boost::mpl::false_ {};
template<class T>
struct placeholder_conversion<T, T> : boost::mpl::true_ {};
template<class T>
struct placeholder_conversion<T, T&> : boost::mpl::true_ {};
template<class T>
struct placeholder_conversion<T, const T&> : boost::mpl::true_ {};
template<class T>
struct placeholder_conversion<const T, T> : boost::mpl::true_ {};
template<class T>
struct placeholder_conversion<const T, const T&> : boost::mpl::true_ {};
template<class T>
struct placeholder_conversion<T&, T> : boost::mpl::true_ {};
template<class T>
struct placeholder_conversion<T&, T&> : boost::mpl::true_ {};
template<class T>
struct placeholder_conversion<T&, const T&> : boost::mpl::true_ {};
template<class T>
struct placeholder_conversion<const T&, T> : boost::mpl::true_ {};
template<class T>
struct placeholder_conversion<const T&, const T&> : boost::mpl::true_ {};
#ifndef BOOST_NO_CXX11_RVALUE_REFERENCES
template<class T>
struct placeholder_conversion<T&&, T> : boost::mpl::true_ {};
template<class T>
struct placeholder_conversion<T&&, const T&> : boost::mpl::true_ {};
template<class T>
struct placeholder_conversion<T&&, T&&> : boost::mpl::true_ {};
#endif
}
#ifdef __clang__
#if !__has_feature(cxx_reference_qualified_functions)
/** INTERNAL ONLY */
#define BOOST_NO_FUNCTION_REFERENCE_QUALIFIERS
#endif
#else
/** INTERNAL ONLY */
#define BOOST_NO_FUNCTION_REFERENCE_QUALIFIERS
#endif
/**
* \brief A wrapper to help with overload resolution for functions
* operating on an @ref any.
*
* The template arguments are interpreted in
* the same way as @ref any.
*
* A parameter of type @ref param can be initialized
* with an @ref any that has the same @c Concept
* and base placeholder when there exists a corresponding
* standard conversion for the placeholder.
* A conversion sequence from @ref any<C, P> to @ref param<C, P1> is
* a better conversion sequence than @ref any<C, P> to @ref param<C, P2>
* iff the corresponding placeholder standard conversion
* sequence from P to P1 is a better conversion sequence than
* P to P2.
*
* \note Overloading based on cv-qualifiers and rvalue-ness is
* only supported in C++11. In C++03, all conversion sequences
* from @ref any to @ref param have the same rank.
*
* Example:
*
* \code
* void f(param<C, _a&>);
* void f(param<C, const _a&>);
* void g(param<C, const _a&>);
* void g(param<C, _a&&>);
*
* any<C, _a> a;
* f(any<C, _a>()); // calls void f(param<C, const _a&>);
* f(a); // calls void f(param<C, _a&>); (ambiguous in C++03)
* g(any<C, _a>()); // calls void g(param<C, _a&&>); (ambiguous in C++03)
* g(a); // calls void g(param<C, const _a&>);
* \endcode
*
*/
template<class Concept, class T>
class param {
public:
friend struct boost::type_erasure::detail::access;
/** INTERNAL ONLY */
typedef void _boost_type_erasure_is_any;
/** INTERNAL ONLY */
typedef param _boost_type_erasure_derived_type;
template<class U>
param(any<Concept, U>& a
#ifndef BOOST_TYPE_ERASURE_DOXYGEN
, typename boost::enable_if<
::boost::type_erasure::detail::placeholder_conversion<U, T>
>::type* = 0
#endif
)
: _impl(a)
{}
template<class U>
param(const any<Concept, U>& a
#ifndef BOOST_TYPE_ERASURE_DOXYGEN
, typename boost::enable_if<
::boost::type_erasure::detail::placeholder_conversion<
typename ::boost::add_const<U>::type,
T
>
>::type* = 0
#endif
)
: _impl(a)
{}
#ifndef BOOST_NO_CXX11_RVALUE_REFERENCES
template<class U>
param(any<Concept, U>&& a
#ifndef BOOST_TYPE_ERASURE_DOXYGEN
, typename boost::enable_if<
::boost::type_erasure::detail::placeholder_conversion<
U&&,
T
>
>::type* = 0
#endif
)
: _impl(std::move(a))
{}
#endif
/** Returns the stored @ref any. */
any<Concept, T> get() const { return _impl; }
private:
any<Concept, T> _impl;
};
#ifndef BOOST_NO_FUNCTION_REFERENCE_QUALIFIERS
template<class Concept, class T>
class param<Concept, const T&> {
public:
friend struct boost::type_erasure::detail::access;
/** INTERNAL ONLY */
typedef void _boost_type_erasure_is_any;
/** INTERNAL ONLY */
typedef param _boost_type_erasure_derived_type;
param(const ::boost::type_erasure::detail::storage& data,
const ::boost::type_erasure::binding<Concept>& table)
: _impl(data, table)
{}
template<class U>
param(U& u, typename boost::enable_if< ::boost::is_same<U, const any<Concept, T> > >::type* = 0) : _impl(u) {}
any<Concept, const T&> get() const { return _impl; }
protected:
any<Concept, const T&> _impl;
};
template<class Concept, class T>
class param<Concept, T&> : public param<Concept, const T&> {
public:
friend struct boost::type_erasure::detail::access;
/** INTERNAL ONLY */
typedef void _boost_type_erasure_is_any;
/** INTERNAL ONLY */
typedef param _boost_type_erasure_derived_type;
param(const ::boost::type_erasure::detail::storage& data,
const ::boost::type_erasure::binding<Concept>& table)
: param<Concept, const T&>(data, table)
{}
any<Concept, T&> get() const
{
return any<Concept, T&>(
::boost::type_erasure::detail::access::data(this->_impl),
::boost::type_erasure::detail::access::table(this->_impl));
}
};
#ifndef BOOST_NO_CXX11_RVALUE_REFERENCES
template<class Concept, class T>
class param<Concept, T&&> : public param<Concept, const T&> {
public:
friend struct boost::type_erasure::detail::access;
/** INTERNAL ONLY */
typedef void _boost_type_erasure_is_any;
/** INTERNAL ONLY */
typedef param _boost_type_erasure_derived_type;
param(const ::boost::type_erasure::detail::storage& data,
const ::boost::type_erasure::binding<Concept>& table)
: param<Concept, const T&>(data, table)
{}
any<Concept, T&&> get() const
{
return any<Concept, T&&>(
::boost::type_erasure::detail::access::data(this->_impl),
::boost::type_erasure::detail::access::table(this->_impl));
}
};
#endif
#endif
/**
* \brief Metafunction that creates a @ref param.
*
* If @c T is a (cv/reference qualifed) placeholder,
* returns @ref param<@ref concept_of "concept_of<Any>::type", T>,
* otherwise, returns T. This metafunction is intended
* to be used for function arguments in specializations of
* @ref concept_interface.
*
* \see derived, rebind_any
*/
template<class Any, class T>
struct as_param {
#ifdef BOOST_TYPE_ERASURE_DOXYGEN
typedef detail::unspecified type;
#else
typedef typename ::boost::mpl::if_<
::boost::type_erasure::is_placeholder<
typename ::boost::remove_cv<
typename ::boost::remove_reference<T>::type>::type>,
param<typename ::boost::type_erasure::concept_of<Any>::type, T>,
T
>::type type;
#endif
};
}
}
#endif