bslmf_removeconst.h

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/// @file bslmf_removeconst.h
///
/// The content of this file has been pre-processed for Doxygen.
///
 
 
// bslmf_removeconst.h                                                -*-C++-*-
#ifndef INCLUDED_BSLMF_REMOVECONST
#define INCLUDED_BSLMF_REMOVECONST
 
#include <bsls_ident.h>
BSLS_IDENT("$Id: $")
 
/// @defgroup bslmf_removeconst bslmf_removeconst
/// @brief  Provide a meta-function for removing top-level `const`-qualifier.
/// @addtogroup bsl
/// @{
/// @addtogroup bslmf
/// @{
/// @addtogroup bslmf_removeconst
/// @{
///
/// <h1> Outline </h1>
/// * <a href="#bslmf_removeconst-purpose"> Purpose</a>
/// * <a href="#bslmf_removeconst-classes"> Classes </a>
/// * <a href="#bslmf_removeconst-description"> Description </a>
///   * <a href="#bslmf_removeconst-usage"> Usage </a>
///     * <a href="#bslmf_removeconst-example-1-removing-the-const-qualifier-of-a-type"> Example 1: Removing the const-Qualifier of a Type </a>
///
/// # Purpose {#bslmf_removeconst-purpose}
/// Provide a meta-function for removing top-level `const`-qualifier.
///
/// # Classes {#bslmf_removeconst-classes}
///
/// -  bsl::remove_const: meta-function for removing top-level `const`-qualifier
/// -  bsl::remove_const_t: alias to the return type of the `bsl::remove_const`
///
/// @see  bslmf_addconst
///
/// # Description {#bslmf_removeconst-description}
/// This component defines a meta-function, `bsl::remove_const` and
/// declares an `bsl::remove_const_t` alias to the return type of the
/// `bsl::remove_const`, that may be used to remove any top-level
/// `const`-qualifier from a type.
///
/// `bsl::remove_const` and `bsl::remove_const_t` meet the requirements of the
/// @ref remove_const  template defined in the C++11 standard [meta.trans.cv].
///
/// ## Usage {#bslmf_removeconst-usage}
///
///
/// In this section we show intended use of this component.
///
/// ### Example 1: Removing the const-Qualifier of a Type {#bslmf_removeconst-example-1-removing-the-const-qualifier-of-a-type}
///
///
/// Suppose that we want to remove any top-level `const`-qualifier from a
/// particular type.
///
/// First, we create two `typedef`s -- a `const`-qualified type (`MyConstType`)
/// and the same type without the `const`-qualifier (`MyType`):
/// @code
/// typedef int       MyType;
/// typedef const int MyConstType;
/// @endcode
/// Now, we remove the `const`-qualifier from `MyConstType` using
/// `bsl::remove_const` and verify that the resulting type is the same as
/// `MyType`:
/// @code
/// assert(true ==
///       (bsl::is_same<bsl::remove_const<MyConstType>::type, MyType>::value));
/// @endcode
/// Finally, if the current compiler supports alias templates C++11 feature, we
/// remove a `const`-qualifier from `MyConstType` using `bsl::remove_const_t`
/// and verify that the resulting type is the same as `MyType`:
/// @code
/// #ifdef BSLS_COMPILERFEATURES_SUPPORT_ALIAS_TEMPLATES
///   assert(true ==
///             (bsl::is_same<bsl::remove_const_t<MyConstType>, MyType>::value));
/// #endif
/// @endcode
/// Note, that the `bsl::remove_const_t` avoids the `::type` suffix and
/// `typename` prefix when we want to use the result of the `bsl::remove_const`
/// meta-function in templates.
/// @}
/** @} */
/** @} */
 
/** @addtogroup bsl
 * @{
 */
/** @addtogroup bslmf
 * @{
 */
/** @addtogroup bslmf_removeconst
 * @{
 */
 
#include <bslscm_version.h>
 
#include <bsls_compilerfeatures.h>
#include <bsls_platform.h>
 
#include <stddef.h>
 
 
// Several compiler tool-chains have problems removing the const qualifiers
// from arrays.  Additional documentation is below (where these macros are
// used).
#if defined(BSLS_PLATFORM_CMP_IBM)
 
# define BSLS_REMOVECONST_WORKAROUND_CONST_MULTIDIMENSIONAL_ARRAY 1
    // The IBM xlC compiler has an odd issue trying to remove 'const'
    // qualifiers from multidimensional arrays.  This workaround was last
    // verified as required for the xlC 12.1 compiler - more recent compilers
    // still need testing.
 
#elif (defined(BSLS_PLATFORM_CMP_SUN) && BSLS_PLATFORM_CMP_VERSION < 0x5130)  \
   || (defined(BSLS_PLATFORM_CMP_MSVC)                                        \
            && BSLS_PLATFORM_CMP_VERSION <= 1900                              \
            && _MSC_FULL_VER < 190023918)
 
# define BSLS_REMOVECONST_WORKAROUND_CONST_ARRAY 1
    // The Microsoft compiler does not recognize array-types as cv-qualified
    // when the element type is cv-qualified when performing matching for
    // partial template specialization, but does get the correct result when
    // performing overload resolution for functions (taking arrays by
    // reference).  Given the function dispatch behavior being correct, we
    // choose to work around this compiler bug, rather than try to report
    // compiler behavior, as the compiler itself is inconsistent depending on
    // how the trait might be used.  This also corresponds to how Microsoft
    // itself implements the trait in VC2010 and later.  Note that Microsoft
    // fixed this bug in Update 2 for MSVC2015, which requires checking the
    // '_MSC_FULL_VER' macro; the workaround below would be ambiguous when
    // trying to remove 'const' from an array of 'const' elements with a
    // conforming compiler.
 
#endif
 
namespace bsl {
 
                         // ===================
                         // struct remove_const
                         // ===================
 
/// This `struct` template implements the @ref remove_const  meta-function
/// defined in the C++11 standard [meta.trans.cv], providing an alias,
/// `type`, that returns the result.  `type` has the same type as the
/// (template parameter) `t_TYPE` except that any top-level
/// `const`-qualifier has been removed.  Note that this generic default
/// template provides a `type` that is an alias to `t_TYPE` for when
/// `t_TYPE` is not `const`-qualified.  A template specialization is
/// provided (below) that removes the `const`-qualifier for when `t_TYPE` is
/// `const`-qualified.
template <class t_TYPE>
struct remove_const {
 
    // PUBLIC TYPES
 
    /// This `typedef` is an alias to the (template parameter) `t_TYPE`.
    typedef t_TYPE type;
};
 
                     // =================================
                     // struct remove_const<t_TYPE const>
                     // =================================
 
/// This partial specialization of `bsl::remove_const`, for when the
/// (template parameter) `t_TYPE` is `const`-qualified, provides a
/// `typedef`, `type`, that has the `const`-qualifier removed.
template <class t_TYPE>
struct remove_const<t_TYPE const> {
 
    // PUBLIC TYPES
 
    /// This `typedef` is an alias to the same type as the (template
    /// parameter) `t_TYPE` except with the `const`-qualifier removed.
    typedef t_TYPE type;
};
 
#if defined(BSLS_REMOVECONST_WORKAROUND_CONST_MULTIDIMENSIONAL_ARRAY)
template <class t_TYPE, size_t N>
struct remove_const<t_TYPE[N]> {
    // This partial specialization of 'bsl::remove_const', for when the
    // (template parameter) 't_TYPE' is an array type.  On IBM compilers, it is
    // necessary to separately @ref remove_const  on the element type, and then
    // reconstruct the array dimensions.
 
    // PUBLIC TYPES
    typedef typename remove_const<t_TYPE>::type type[N];
        // This 'typedef' is an alias to the same type as the (template
        // parameter) 't_TYPE[N]' except with the 'const'-qualifier removed.
};
 
template <class t_TYPE, size_t N>
struct remove_const<const t_TYPE[N]> {
    // This partial specialization of 'bsl::remove_const', for when the
    // (template parameter) 't_TYPE' is an array type.  On IBM compilers, it is
    // necessary to separately @ref remove_const  on the element type, and then
    // reconstruct the array dimensions.
 
    // PUBLIC TYPES
    typedef typename remove_const<const t_TYPE>::type type[N];
        // This 'typedef' is an alias to the same type as the (template
        // parameter) 't_TYPE[N]' except with the 'const'-qualifier removed.
};
 
template <class t_TYPE>
struct remove_const<t_TYPE[]> {
    // This partial specialization of 'bsl::remove_const', for when the
    // (template parameter) 't_TYPE' is an array type.  On IBM compilers, it is
    // necessary to separately @ref remove_const  on the element type, and then
    // reconstruct the array dimensions.
 
    // PUBLIC TYPES
    typedef typename remove_const<t_TYPE>::type type[];
        // This 'typedef' is an alias to the same type as the (template
        // parameter) 't_TYPE[]' except with the 'const'-qualifier removed.
};
 
template <class t_TYPE>
struct remove_const<const t_TYPE[]> {
    // This partial specialization of 'bsl::remove_const', for when the
    // (template parameter) 't_TYPE' is an array type.  On IBM compilers, it is
    // necessary to separately @ref remove_const  on the element type, and then
    // reconstruct the array dimensions.
 
    // PUBLIC TYPES
    typedef typename remove_const<const t_TYPE>::type type[];
        // This 'typedef' is an alias to the same type as the (template
        // parameter) 't_TYPE[]' except with the 'const'-qualifier removed.
};
#elif defined(BSLS_REMOVECONST_WORKAROUND_CONST_ARRAY)
template <class t_TYPE>
struct remove_const<t_TYPE[]> {
    // This partial specialization of 'bsl::remove_const', for when the
    // (template parameter) 't_TYPE' is an array type.  On Microsoft compilers,
    // it is necessary to separately @ref remove_const  on the element type, and
    // then reconstruct the array dimensions.
 
    // PUBLIC TYPES
    typedef typename remove_const<t_TYPE>::type type[];
        // This 'typedef' is an alias to the same type as the (template
        // parameter) 't_TYPE[]' except with the 'const'-qualifier removed.
};
 
template <class t_TYPE, size_t LENGTH>
struct remove_const<t_TYPE[LENGTH]> {
    // This partial specialization of 'bsl::remove_const', for when the
    // (template parameter) 't_TYPE' is an array type.  On Microsoft compilers,
    // it is necessary to separately @ref remove_const  on the element type, and
    // then reconstruct the array dimensions.
 
    // PUBLIC TYPES
    typedef typename remove_const<t_TYPE>::type type[LENGTH];
        // This 'typedef' is an alias to the same type as the (template
        // parameter) 't_TYPE[N]' except with the 'const'-qualifier removed.
};
#endif
 
#ifdef BSLS_COMPILERFEATURES_SUPPORT_ALIAS_TEMPLATES
 
// ALIASES
 
/// `remove_const_t` is an alias to the return type of the
/// `bsl::remove_const` meta-function.  Note, that the `remove_const_t`
/// avoids the `::type` suffix and `typename` prefix when we want to use the
/// result of the meta-function in templates.
template <class t_TYPE>
using remove_const_t = typename remove_const<t_TYPE>::type;
#endif  // BSLS_COMPILERFEATURES_SUPPORT_ALIAS_TEMPLATES
 
 
}  // close namespace bsl
 
#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 ----------------------------------
 
/** @} */
/** @} */
/** @} */