bslmf_usesallocator.h

Go to the documentation of this file.

/// @file bslmf_usesallocator.h
///
/// The content of this file has been pre-processed for Doxygen.
///
 
 
// bslmf_usesallocator.h                                              -*-C++-*-
#ifndef INCLUDED_BSLMF_USESALLOCATOR
#define INCLUDED_BSLMF_USESALLOCATOR
 
#include <bsls_ident.h>
BSLS_IDENT("$Id: $")
 
/// @defgroup bslmf_usesallocator bslmf_usesallocator
/// @brief  Provide a meta-function to determine if a type uses an allocator.
/// @addtogroup bsl
/// @{
/// @addtogroup bslmf
/// @{
/// @addtogroup bslmf_usesallocator
/// @{
///
/// <h1> Outline </h1>
/// * <a href="#bslmf_usesallocator-purpose"> Purpose</a>
/// * <a href="#bslmf_usesallocator-classes"> Classes </a>
/// * <a href="#bslmf_usesallocator-description"> Description </a>
///   * <a href="#bslmf_usesallocator-usage"> Usage </a>
///     * <a href="#bslmf_usesallocator-example-1-determine-if-a-type-uses-an-allocator"> Example 1: Determine If a Type Uses an Allocator </a>
///
/// # Purpose {#bslmf_usesallocator-purpose}
/// Provide a meta-function to determine if a type uses an allocator.
///
/// # Classes {#bslmf_usesallocator-classes}
///
/// -  bsl::uses_allocator: meta-fn to check if a type uses a certain allocator
/// -  bsl::uses_allocator_v: the result value of `bsl::uses_allocator`
///
/// @see  bslmf_isconvertible
///
/// # Description {#bslmf_usesallocator-description}
/// This component defines a meta-function, `bsl::uses_allocator`,
/// that may be used to query whether a given type uses a given allocator type.
///
/// `bsl::uses_allocator` meets the requirements of the @ref uses_allocator 
/// template defined in the C++11 standard [allocator.uses.trait], in addition
/// to providing a welcome availability in both C++03 and C++11 compilation
/// environments.
///
/// A type `T` uses an allocator type `A` if `T` has a nested alias named
/// `allocator_type` and `A` is convertible to `allocator_type` (as defined in
/// the @ref bslmf_isconvertible  component).  If a type `T` uses an allocator type
/// `A`, then `T` has a constructor that takes either 1) @ref allocator_arg_t  as a
/// first argument and `A` as a second argument, or 2) `A` as the last argument.
/// Alternatively, the @ref uses_allocator  template may be specialized for a type
/// `T` that does not have a nested alias named `allocator_type`, where `T` can
/// be constructed with `A` as detailed above.
///
/// Note that the template variable @ref uses_allocator_v  is defined in the C++17
/// standard as an inline variable.  If the current compiler supports the inline
/// variable C++17 compiler feature, `bsl::uses_allocator_v` is defined as an
/// `inline constexpr bool` variable.  Otherwise, if the compiler supports the
/// variable templates C++14 compiler feature, `bsl::uses_allocator_v` is
/// defined as a non-inline `constexpr bool` variable.  See
/// `BSLS_COMPILERFEATURES_SUPPORT_INLINE_VARIABLES` and
/// `BSLS_COMPILERFEATURES_SUPPORT_VARIABLE_TEMPLATES` macros in
/// bsls_compilerfeatures component for details.
///
/// ## Usage {#bslmf_usesallocator-usage}
///
///
/// In this section we show intended use of this component.
///
/// TBD: finish up usage example, add to test driver.
///
/// ### Example 1: Determine If a Type Uses an Allocator {#bslmf_usesallocator-example-1-determine-if-a-type-uses-an-allocator}
///
///
///
/// @code
/// template <class CONTAINER>
/// class ContainerAdaptor {
///     // ...
///   public:
///     ContainerAdaptor();
///         // Create an empty container adaptor.  No allocator will be provided
///         // to the underlying container, and the container's memory
///         // allocation will be provided by whatever is the default for the
///         // container type.
///
///     template <class t_ALLOC>
///     explicit
///     ContainerAdaptor(const t_ALLOC& basicAllocator,
///                      typename bsl::enable_if<
///                              bsl::uses_allocator<CONTAINER, t_ALLOC>::value,
///                              t_ALLOC>::type * = 0);
///         // Create an empty container adaptor, and use the specified
///         // 'basicAllocator' to supply memory.  Note that this constructor is
///         // available only when the type of the argument is compatible with
///         // the allocator type associated with the container.
///
///     // ...
/// };
/// @endcode
///
/// @}
/** @} */
/** @} */
 
/** @addtogroup bsl
 * @{
 */
/** @addtogroup bslmf
 * @{
 */
/** @addtogroup bslmf_usesallocator
 * @{
 */
 
#include <bslscm_version.h>
 
#include <bslmf_integralconstant.h>
#include <bslmf_isconvertible.h>
#include <bslmf_voidtype.h>
 
#include <bsls_compilerfeatures.h>
#include <bsls_keyword.h>
 
 
namespace bslmf {
 
/// This `struct` template derives from `bsl::false_type` when the (template
/// parameter) type `t_TYPE` does not have a nested alias `allocator_type`.
template <class t_TYPE, class t_ALLOC, class = void>
struct UsesAllocator_Imp : bsl::false_type {
};
 
/// This `struct` template derives from `bsl::true_type` when the (template
/// parameter) `t_TYPE` has a nested alias `allocator_type` and the
/// (template parameter) type `t_ALLOC` is convertible to
/// `t_TYPE::allocator_type`, and `bsl::false_type` otherwise.
template <class t_TYPE, class t_ALLOC>
struct UsesAllocator_Imp<t_TYPE,
                         t_ALLOC,
                         BSLMF_VOIDTYPE(typename t_TYPE::allocator_type)>
: bsl::is_convertible<t_ALLOC, typename t_TYPE::allocator_type>::type {
};
 
}  // close package namespace
 
 
namespace bsl {
 
                        // =====================
                        // struct uses_allocator
                        // =====================
 
/// This `struct` template implements a meta-function to determine whether a
/// (template parameter) `t_TYPE` uses a given (template parameter)
/// `t_ALLOCATOR_TYPE`.  This `struct` derives from `bsl::true_type` if
/// `t_TYPE` uses `t_ALLOCATOR_TYPE` and from `bsl::false_type` otherwise.
/// This meta-function has the same syntax as the @ref uses_allocator 
/// meta-function defined in the C++11 standard [allocator.uses.trait].
template <class t_TYPE, class t_ALLOCATOR_TYPE>
struct uses_allocator
: BloombergLP::bslmf::UsesAllocator_Imp<t_TYPE, t_ALLOCATOR_TYPE>::type {
};
 
#ifdef BSLS_COMPILERFEATURES_SUPPORT_VARIABLE_TEMPLATES
/// This template variable represents the result value of the
/// `bsl::uses_allocator` meta-function.
template <class t_TYPE, class t_ALLOCATOR_TYPE>
BSLS_KEYWORD_INLINE_VARIABLE constexpr bool uses_allocator_v =
                               uses_allocator<t_TYPE, t_ALLOCATOR_TYPE>::value;
#endif
 
 
}  // close namespace bsl
 
#endif
 
// ----------------------------------------------------------------------------
// Copyright 2019 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 ----------------------------------
 
/** @} */
/** @} */
/** @} */