text: // bslmf_isvolatile.h                                                 -*-C++-*-
  #ifndef INCLUDED_BSLMF_ISVOLATILE
  #define INCLUDED_BSLMF_ISVOLATILE
  
  #include <bsls_ident.h>
  BSLS_IDENT("$Id: $")
  
  //@PURPOSE: Provide a compile-time check for 'volatile'-qualified types.
  //
  //@CLASSES:
  //  bsl::is_volatile: meta-function for determining 'volatile'-qualified types
  //  bsl::is_volatile_v: the result value of 'bsl::is_volatile'
  //
  //@SEE_ALSO: bslmf_integralconstant
  //
  //@DESCRIPTION: This component defines a meta-function, 'bsl::is_volatile' and
  // a template variable 'bsl::is_volatile_v', that represents the result value
  // of the meta-function, that may be used to query whether a type is
  // 'volatile'-qualified as defined in the C++11 standard
  // [basic.type.qualifier].
  //
  // 'bsl::is_volatile' meets the requirements of the 'is_volatile' template
  // defined in the C++11 standard [meta.unary.prop].
  //
  // Note that the template variable 'is_volatile_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::is_volatile_v' is defined as an
  // 'inline constexpr bool' variable.  Otherwise, if the compiler supports the
  // variable templates C++14 compiler feature, 'bsl::is_volatile_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
  ///-----
  // In this section we show intended use of this component.
  //
  ///Example 1: Verify 'volatile' Types
  ///- - - - - - - - - - - - - - - -
  // Suppose that we want to assert whether a particular type is
  // 'volatile'-qualified.
  //
  // First, we create two 'typedef's -- a 'volatile'-qualified type and an
  // unqualified type:
  //..
  //  typedef int           MyType;
  //  typedef volatile int  MyVolatileType;
  //..
  // Now, we instantiate the 'bsl::is_volatile' template for each of the
  // 'typedef's and assert the 'value' static data member of each instantiation:
  //..
  //  assert(false == bsl::is_volatile<MyType>::value);
  //  assert(true  == bsl::is_volatile<MyVolatileType>::value);
  //..
  // Note that if the current compiler supports the variable templates C++14
  // feature, then we can re-write the snippet of code above as follows:
  //..
  //  #ifdef BSLS_COMPILERFEATURES_SUPPORT_VARIABLE_TEMPLATES
  //  assert(false == bsl::is_volatile_v<MyType>);
  //  assert(true  == bsl::is_volatile_v<MyVolatileType>);
  //  #endif
  //..
  
  #include <bslscm_version.h>
  
  #include <bslmf_integralconstant.h>
  #include <bslmf_issame.h>
  
  #include <bsls_platform.h>
  #include <bsls_compilerfeatures.h>
  #include <bsls_keyword.h>
  
  #include <stddef.h>
  
  
  #if (defined(BSLS_PLATFORM_CMP_MSVC) && BSLS_PLATFORM_CMP_VERSION < 1910)     \
   ||  defined(BSLS_PLATFORM_CMP_IBM)
  // 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 Microsft itself implements the trait in VC2010 and later.
  # define BSLMF_ISVOLATILE_COMPILER_DOES_NOT_DETECT_CV_QUALIFIED_ARRAY_ELEMENT 1
  #endif
  
  namespace bsl {
  
                           // ==================
                           // struct is_volatile
                           // ==================
  
  template <class TYPE>
  struct is_volatile : false_type {
      // This 'struct' template implements the 'is_volatile' meta-function
      // defined in the C++11 standard [meta.unary.cat] to determine if the
      // (template parameter) 'TYPE' is 'volatile'-qualified.  This 'struct'
      // derives from 'bsl::true_type' if the 'TYPE' is 'volatile'-qualified, and
      // 'bsl::false_type' otherwise.  Note that this generic default template
      // derives from 'bsl::false_type'.  A template specialization is provided
      // (below) that derives from 'bsl::true_type'.
  };
  
                           // =================================
                           // struct is_volatile<TYPE volatile>
                           // =================================
  
  #if defined(BSLS_PLATFORM_CMP_SUN) && BSLS_PLATFORM_CMP_VERSION < 0x5130
  template <class TYPE>
  struct is_volatile<volatile TYPE>
      : integral_constant<bool, !is_same<TYPE, volatile TYPE>::value> {
       // This partial specialization of 'is_volatile', for when the (template
       // parameter) 'TYPE' is 'volatile'-qualified, derives from
       // 'bsl::true_type'.  Note that the Solaris CC compiler misdiagnoses
       // cv-qualified "abominable" function types as being cv-qualified
       // themselves.  The correct result is obtained by delegating the result to
       // a call through 'is_same'.
  };
  #else
  template <class TYPE>
  struct is_volatile<volatile TYPE> : true_type {
       // This partial specialization of 'is_volatile', for when the (template
       // parameter) 'TYPE' is 'volatile'-qualified, derives from
       // 'bsl::true_type'.
  };
  #endif
  
  
  #ifdef BSLMF_ISVOLATILE_COMPILER_DOES_NOT_DETECT_CV_QUALIFIED_ARRAY_ELEMENT
  // 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 depeoning on how the trait might be used.  This also
  // corresponds to how Microsft itself implements the trait in VC2010 and later.
  
  template <class TYPE>
  struct is_volatile<volatile TYPE[]> : true_type {
       // This partial specialization of 'is_volatile', for when the (template
       // parameter) 'TYPE' is 'volatile'-qualified, derives from
       // 'bsl::true_type'.  Note that this single specialization is sufficient
       // to work around the MSVC issue, even for multidimensional arrays.
  };
  
  template <class TYPE, size_t LENGTH>
  struct is_volatile<volatile TYPE[LENGTH]> : true_type {
       // This partial specialization of 'is_volatile', for when the (template
       // parameter) 'TYPE' is 'volatile'-qualified, derives from
       // 'bsl::true_type'.  Note that this single specialization is sufficient
       // to work around the MSVC issue, even for multidimensional arrays.
  };
  #endif
  
  #ifdef BSLS_COMPILERFEATURES_SUPPORT_VARIABLE_TEMPLATES
  template <class TYPE>
  BSLS_KEYWORD_INLINE_VARIABLE
  constexpr bool is_volatile_v = is_volatile<TYPE>::value;
      // This template variable represents the result value of the
      // 'bsl::is_volatile' meta-function.
  #endif
  
  }  // close namespace bsl
  
  #endif
  
  // ----------------------------------------------------------------------------
  // Copyright 2017 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 ----------------------------------
  
  