bslalg_hastrait.h

Go to the documentation of this file.

/// @file bslalg_hastrait.h
///
/// The content of this file has been pre-processed for Doxygen.
///
 
 
// bslalg_hastrait.h                                                  -*-C++-*-
#ifndef INCLUDED_BSLALG_HASTRAIT
#define INCLUDED_BSLALG_HASTRAIT
 
#include <bsls_ident.h>
BSLS_IDENT("$Id: $")
 
/// @defgroup bslalg_hastrait bslalg_hastrait
/// @brief  Provide a meta-function to detect if a type has a given trait.
/// @addtogroup bsl
/// @{
/// @addtogroup bslalg
/// @{
/// @addtogroup bslalg_hastrait
/// @{
///
/// <h1> Outline </h1>
/// * <a href="#bslalg_hastrait-purpose"> Purpose</a>
/// * <a href="#bslalg_hastrait-classes"> Classes </a>
/// * <a href="#bslalg_hastrait-description"> Description </a>
///   * <a href="#bslalg_hastrait-usage"> Usage </a>
///
/// # Purpose {#bslalg_hastrait-purpose}
/// Provide a meta-function to detect if a type has a given trait.
///
/// @deprecated  Do not use.
///
/// # Classes {#bslalg_hastrait-classes}
///
/// -  bslalg::HasTrait: legacy mechanism for detecting type traits
///
/// @see  bslalg_typetraits, bslmf_integralconstant
///
/// # Description {#bslalg_hastrait-description}
/// This component provides a meta-function, `bslalg::HasTrait`,
/// that is a legacy mechanism for detecting traits.  `bslalg::HasTrait` takes
/// two template parameters, `TYPE` and `TRAIT`.
/// `bslalg::HasTrait<TYPE, TRAIT>` inherits from `bsl::true_type` if the
/// (template parameter) `TYPE` has the (template parameter) `TRAIT`, and
/// inherits from `bsl::false_type` otherwise.
///
/// `bslalg::HasTrait` is *not* a general-purpose trait detection facility.  It
/// is intended to be used in conjunction with the legacy (deprecated) `bslalg`
/// traits only.  In particular, the type supplied to `bslalg::HasTrait` as the
/// `TRAIT` template parameter *must* be a `bslalg` trait, for example,
/// `bslalg::TypeTraitUsesBslmaAllocator`.  Supplying anything else for `TRAIT`
/// will (more than likely) fail to compile.  For example, the following errant
/// use of `bslalg::HasTrait` will definitely fail to compile:
/// @code
/// bslalg::HasTrait<Foo, bsl::is_trivially_default_constructible>'
/// @endcode
/// See @ref bslalg_typetraits  for a complete list of the `bslalg` traits that are
/// supported by `bslalg::HasTrait`.
///
/// In lieu of the deprecated `bslalg` traits, the newer traits intended to
/// replace them should be used instead.  These successor traits are typically
/// defined in `bslmf` (two exceptions are `bslma::UsesBslmaAllocator` and
/// `bslalg::HasStlIterators`).  `bslalg::HasTrait` and the `bslalg` traits that
/// it supports are written in such a way that `bslalg::HasTrait` will correctly
/// detect whether a type has a given trait regardless of whether the trait is
/// ascribed to the type using the deprecated `BSLALG_DECLARE_NESTED_TRAITS*` or
/// `BSLMF_NESTED_TRAIT_DECLARATION` macros (see @ref bslalg_typetraits  and
/// @ref bslmf_nestedtraitdeclaration , respectively), or whether the (preferred)
/// C++11 idiom for defining traits is used (see @ref bslmf_detectnestedtrait ).  In
/// this way, `bslalg::HasTrait` provides a "bridge" between legacy `bslalg`
/// type traits and their replacements that facilitates the migration to the
/// newer traits.
///
/// ## Usage {#bslalg_hastrait-usage}
///
///
/// No Usage example is provided since this component is deprecated.
/// @}
/** @} */
/** @} */
 
/** @addtogroup bsl
 * @{
 */
/** @addtogroup bslalg
 * @{
 */
/** @addtogroup bslalg_hastrait
 * @{
 */
 
#include <bslscm_version.h>
 
#include <bslmf_integralconstant.h>
#include <bslmf_removecv.h>
 
#ifndef BDE_DONT_ALLOW_TRANSITIVE_INCLUDES
#include <bslmf_isconvertible.h>
#include <bslmf_removecvq.h>
#endif // BDE_DONT_ALLOW_TRANSITIVE_INCLUDES
 
 
namespace bslalg {
 
                       // ===============
                       // struct HasTrait
                       // ===============
 
/// This meta-function evaluates to `bsl::true_type` if the (template
/// parameter) `TYPE` has the (template parameter) `TRAIT`, and to
/// `bsl::false_type` otherwise.
template <class TYPE, class TRAIT>
struct HasTrait : public bsl::integral_constant<
                      bool,
                      TRAIT::template Metafunction<
                          typename bsl::remove_cv<TYPE>::type>::value> {
};
 
}  // close package namespace
 
#ifndef BDE_OPENSOURCE_PUBLICATION  // BACKWARD_COMPATIBILITY
// ============================================================================
//                           BACKWARD COMPATIBILITY
// ============================================================================
 
#ifdef bslalg_HasTrait
#undef bslalg_HasTrait
#endif
/// This alias is defined for backward compatibility.
#define bslalg_HasTrait bslalg::HasTrait
#endif  // BDE_OPENSOURCE_PUBLICATION -- BACKWARD_COMPATIBILITY
 
 
 
#endif
 
// ----------------------------------------------------------------------------
// Copyright 2013 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 ----------------------------------
 
/** @} */
/** @} */
/** @} */