bslmf_usesallocatorargt.h

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/// @file bslmf_usesallocatorargt.h
///
/// The content of this file has been pre-processed for Doxygen.
///
 
 
// bslmf_usesallocatorargt.h                                          -*-C++-*-
#ifndef INCLUDED_BSLMF_USESALLOCATORARGT
#define INCLUDED_BSLMF_USESALLOCATORARGT
 
#include <bsls_ident.h>
BSLS_IDENT("$Id: $")
 
/// @defgroup bslmf_usesallocatorargt bslmf_usesallocatorargt
/// @brief  Provide a metafunction for `allocator_arg_t` construction
/// @addtogroup bsl
/// @{
/// @addtogroup bslmf
/// @{
/// @addtogroup bslmf_usesallocatorargt
/// @{
///
/// <h1> Outline </h1>
/// * <a href="#bslmf_usesallocatorargt-purpose"> Purpose</a>
/// * <a href="#bslmf_usesallocatorargt-classes"> Classes </a>
/// * <a href="#bslmf_usesallocatorargt-description"> Description </a>
///   * <a href="#bslmf_usesallocatorargt-usage"> Usage </a>
///
/// # Purpose {#bslmf_usesallocatorargt-purpose}
/// Provide a metafunction for `allocator_arg_t` construction
///
/// # Classes {#bslmf_usesallocatorargt-classes}
///
/// -  bslmf::UsesAllocatorArgT: metafunction for `allocator_arg_t` checking
///
/// @see  bslmf_allocatorargt
///
/// # Description {#bslmf_usesallocatorargt-description}
/// C++11 introduced an idiom for passing allocators to the
/// constructors of classes in situations where putting the allocator as the
/// last argument would have been ambiguous.  For example, in cases where the
/// type and number of arguments is unknown at specification time, it can be
/// difficult or impossible to determine if the last argument should be used as
/// the allocator for the constructed object.
///
/// The idiom adopted is to pass an object of the empty tag class
/// `std::allocator_arg_t` (or `bsl::allocator_arg_t`, within the BSL library)
/// as the first argument in the constructor, followed immediately by the
/// allocator argument.
///
/// The `UsesAllocatorArgT<T>` metafunction inherits from `true_type` of `T` is
/// one of the classes that uses this idiom; otherwise `false_type`.  It is used
/// when constructing elements of a container or members of a class template, to
/// determine whether and how to pass an allocator to that element or member.
/// By default, any `T` is assumed NOT to use the `allocator_arg_t` idiom.
/// Specialization of this trait is required for classes that do use this idiom.
/// Although a C++11 trait could be designed to automatically determine whether
/// class `T` uses the idiom for a specific set of constructor arguments, such
/// code would not be portable to C++03 compilers, a requirement for BSL
/// classes.
///
/// Given a type `T" where `bslmf::UsesAllocatorArgT<T>::value' is true, if
/// `bslma::UsesBslmaAllocator<T>::value` is also true, then the argument after
/// `allocator_arg` can be of type `bslma::Allocator*`; otherwise, it must be of
/// a type that meets the STL allocator requirements.
///
/// ## Usage {#bslmf_usesallocatorargt-usage}
///
///
/// @}
/** @} */
/** @} */
 
/** @addtogroup bsl
 * @{
 */
/** @addtogroup bslmf
 * @{
 */
/** @addtogroup bslmf_usesallocatorargt
 * @{
 */
 
#include <bslscm_version.h>
 
#include <bslmf_detectnestedtrait.h>
 
 
 
namespace bslmf {
 
                        // ================================
                        // class template UsesAllocatorArgT
                        // ================================
 
/// User-specialized trait type indicating that the constructor of `t_TYPE`
/// can be invoked using `bsl::allocator_arg` as its first argument and an
/// allocator object as its second argument.
template <class t_TYPE>
struct UsesAllocatorArgT : DetectNestedTrait<t_TYPE, UsesAllocatorArgT>::type {
};
 
/// Trait metafunction that determines whether the constructor of `t_TYPE`
/// can be invoked using `bsl::allocator_arg` as its first argument and an
/// allocator object as its second argument.  The value is computed by
/// stripping off the cv-qualifier and forwading to
/// `UsesAllocatorArgT<t_TYPE>`, which is user-specialized for the
/// appropriate types.
template <class t_TYPE>
struct UsesAllocatorArgT<const t_TYPE> : UsesAllocatorArgT<t_TYPE>::type {
};
 
/// Trait metafunction that determines whether the constructor of `t_TYPE`
/// can be invoked using `bsl::allocator_arg` as its first argument and an
/// allocator object as its second argument.  The value is computed by
/// stripping off the cv-qualifier and forwading to
/// `UsesAllocatorArgT<t_TYPE>`, which is user-specialized for the
/// appropriate types.
template <class t_TYPE>
struct UsesAllocatorArgT<volatile t_TYPE> : UsesAllocatorArgT<t_TYPE>::type {
};
 
/// Trait metafunction that determines whether the constructor of `t_TYPE`
/// can be invoked using `bsl::allocator_arg` as its first argument and an
/// allocator object as its second argument.  The value is computed by
/// stripping off the cv-qualifier and forwading to
/// `UsesAllocatorArgT<t_TYPE>`, which is user-specialized for the
/// appropriate types.
template <class t_TYPE>
struct UsesAllocatorArgT<const volatile t_TYPE>
: UsesAllocatorArgT<t_TYPE>::type {
};
 
}  // close package namespace
 
 
 
#endif // ! defined(INCLUDED_BSLMF_USESALLOCATORARGT)
 
// ----------------------------------------------------------------------------
// Copyright 2016 Bloomberg Finance L.P.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// ----------------------------- END-OF-FILE ----------------------------------
 
/** @} */
/** @} */
/** @} */