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//////////////////////////////////////////////////////////////////////////////
//
// (C) Copyright Ion Gaztanaga 2011-2013. 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)
//
// See http://www.boost.org/libs/container for documentation.
//
//////////////////////////////////////////////////////////////////////////////
#ifndef BOOST_CONTAINER_USES_ALLOCATOR_HPP
#define BOOST_CONTAINER_USES_ALLOCATOR_HPP
#include <boost/container/uses_allocator_fwd.hpp>
#include <boost/container/detail/type_traits.hpp>
namespace boost {
namespace container {
//! <b>Remark</b>: if a specialization constructible_with_allocator_suffix<X>::value is true, indicates that T may be constructed
//! with an allocator as its last constructor argument. Ideally, all constructors of T (including the
//! copy and move constructors) should have a variant that accepts a final argument of
//! allocator_type.
//!
//! <b>Requires</b>: if a specialization constructible_with_allocator_suffix<X>::value is true, T must have a nested type,
//! allocator_type and at least one constructor for which allocator_type is the last
//! parameter. If not all constructors of T can be called with a final allocator_type argument,
//! and if T is used in a context where a container must call such a constructor, then the program is
//! ill-formed.
//!
//! <code>
//! template <class T, class Allocator = allocator<T> >
//! class Z {
//! public:
//! typedef Allocator allocator_type;
//!
//! // Default constructor with optional allocator suffix
//! Z(const allocator_type& a = allocator_type());
//!
//! // Copy constructor and allocator-extended copy constructor
//! Z(const Z& zz);
//! Z(const Z& zz, const allocator_type& a);
//! };
//!
//! // Specialize trait for class template Z
//! template <class T, class Allocator = allocator<T> >
//! struct constructible_with_allocator_suffix<Z<T,Allocator> >
//! { static const bool value = true; };
//! </code>
//!
//! <b>Note</b>: This trait is a workaround inspired by "N2554: The Scoped A Model (Rev 2)"
//! (Pablo Halpern, 2008-02-29) to backport the scoped allocator model to C++03, as
//! in C++03 there is no mechanism to detect if a type can be constructed from arbitrary arguments.
//! Applications aiming portability with several compilers should always define this trait.
//!
//! In conforming C++11 compilers or compilers supporting SFINAE expressions
//! (when BOOST_NO_SFINAE_EXPR is NOT defined), this trait is ignored and C++11 rules will be used
//! to detect if a type should be constructed with suffix or prefix allocator arguments.
template <class T>
struct constructible_with_allocator_suffix
{ static const bool value = false; };
//! <b>Remark</b>: if a specialization constructible_with_allocator_prefix<X>::value is true, indicates that T may be constructed
//! with allocator_arg and T::allocator_type as its first two constructor arguments.
//! Ideally, all constructors of T (including the copy and move constructors) should have a variant
//! that accepts these two initial arguments.
//!
//! <b>Requires</b>: specialization constructible_with_allocator_prefix<X>::value is true, T must have a nested type,
//! allocator_type and at least one constructor for which allocator_arg_t is the first
//! parameter and allocator_type is the second parameter. If not all constructors of T can be
//! called with these initial arguments, and if T is used in a context where a container must call such
//! a constructor, then the program is ill-formed.
//!
//! <code>
//! template <class T, class Allocator = allocator<T> >
//! class Y {
//! public:
//! typedef Allocator allocator_type;
//!
//! // Default constructor with and allocator-extended default constructor
//! Y();
//! Y(allocator_arg_t, const allocator_type& a);
//!
//! // Copy constructor and allocator-extended copy constructor
//! Y(const Y& yy);
//! Y(allocator_arg_t, const allocator_type& a, const Y& yy);
//!
//! // Variadic constructor and allocator-extended variadic constructor
//! template<class ...Args> Y(Args&& args...);
//! template<class ...Args>
//! Y(allocator_arg_t, const allocator_type& a, BOOST_FWD_REF(Args)... args);
//! };
//!
//! // Specialize trait for class template Y
//! template <class T, class Allocator = allocator<T> >
//! struct constructible_with_allocator_prefix<Y<T,Allocator> >
//! { static const bool value = true; };
//!
//! </code>
//!
//! <b>Note</b>: This trait is a workaround inspired by "N2554: The Scoped Allocator Model (Rev 2)"
//! (Pablo Halpern, 2008-02-29) to backport the scoped allocator model to C++03, as
//! in C++03 there is no mechanism to detect if a type can be constructed from arbitrary arguments.
//! Applications aiming portability with several compilers should always define this trait.
//!
//! In conforming C++11 compilers or compilers supporting SFINAE expressions
//! (when BOOST_NO_SFINAE_EXPR is NOT defined), this trait is ignored and C++11 rules will be used
//! to detect if a type should be constructed with suffix or prefix allocator arguments.
template <class T>
struct constructible_with_allocator_prefix
{ static const bool value = false; };
#ifndef BOOST_CONTAINER_DOXYGEN_INVOKED
namespace container_detail {
template<typename T, typename Allocator>
struct uses_allocator_imp
{
// Use SFINAE (Substitution Failure Is Not An Error) to detect the
// presence of an 'allocator_type' nested type convertilble from Allocator.
private:
typedef char yes_type;
struct no_type{ char dummy[2]; };
// Match this function if T::allocator_type exists and is
// implicitly convertible from Allocator
template <class U>
static yes_type test(typename U::allocator_type);
// Match this function if T::allocator_type exists and it's type is `erased_type`.
template <class U, class V>
static typename container_detail::enable_if
< container_detail::is_same<typename U::allocator_type, erased_type>
, yes_type
>::type test(const V&);
// Match this function if TypeT::allocator_type does not exist or is
// not convertible from Allocator.
template <typename U>
static no_type test(...);
static Allocator alloc; // Declared but not defined
public:
static const bool value = sizeof(test<T>(alloc)) == sizeof(yes_type);
};
} //namespace container_detail {
#endif //#ifndef BOOST_CONTAINER_DOXYGEN_INVOKED
//! <b>Remark</b>: Automatically detects whether T has a nested allocator_type that is convertible from
//! Allocator. Meets the BinaryTypeTrait requirements ([meta.rqmts] 20.4.1). A program may
//! specialize this type to define uses_allocator<X>::value as true for a T of user-defined type if T does not
//! have a nested allocator_type but is nonetheless constructible using the specified Allocator where either:
//! the first argument of a constructor has type allocator_arg_t and the second argument has type Alloc or
//! the last argument of a constructor has type Alloc.
//!
//! <b>Result</b>: uses_allocator<T, Allocator>::value== true if a type T::allocator_type
//! exists and either is_convertible<Alloc, T::allocator_type>::value != false or T::allocator_type
//! is an alias `erased_type`. False otherwise.
template <typename T, typename Allocator>
struct uses_allocator
: container_detail::uses_allocator_imp<T, Allocator>
{};
}} //namespace boost::container
#endif //BOOST_CONTAINER_USES_ALLOCATOR_HPP
|
