// bslmf_islvaluereference.h -*-C++-*- #ifndef INCLUDED_BSLMF_ISLVALUEREFERENCE #define INCLUDED_BSLMF_ISLVALUEREFERENCE #include <bsls_ident.h> BSLS_IDENT("$Id: $") //@PURPOSE: Provide a compile-time check for lvalue reference types. // //@CLASSES: // bsl::is_lvalue_reference: standard meta-function for lvalue reference types // bsl::is_lvalue_reference_v: the result value of the meta-function // //@SEE_ALSO: bslmf_integralconstant // //@DESCRIPTION: This component defines a meta-function, // 'bsl::is_lvalue_reference' and a template variable // 'bsl::is_lvalue_reference_v', that represents the result value of the // 'bsl::is_lvalue_reference' meta-function, that may be used to query whether // a type is an lvalue reference type. // // 'bsl::is_lvalue_reference' meets the requirements of the // 'is_lvalue_reference' template defined in the C++11 standard // [meta.unary.cat]. // // Note that the template variable 'is_lvalue_reference_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_lvalue_reference_v' is // defined as an 'inline constexpr bool' variable. Otherwise, if the compiler // supports the variable templates C++14 compiler feature, // 'bsl::is_lvalue_reference_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 Lvalue Reference Types /// - - - - - - - - - - - - - - - - - - - - // Suppose that we want to assert whether a set of types are lvalue reference // types. // // Now, we instantiate the 'bsl::is_lvalue_reference' template for both a // non-reference type and an lvalue reference type, and assert the 'value' // static data member of each instantiation: //.. // assert(false == bsl::is_lvalue_reference<int>::value); // assert(true == bsl::is_lvalue_reference<int&>::value); //.. // Note that if the current compiler supports the variable templates C++14 // feature then we can re-write the snippet of code above using the // 'bsl::is_lvalue_reference_v' variable as follows: //.. //#ifdef BSLS_COMPILERFEATURES_SUPPORT_VARIABLE_TEMPLATES // assert(false == bsl::is_lvalue_reference_v<int>); // assert(true == bsl::is_lvalue_reference_v<int&>); //#endif //.. #include <bslscm_version.h> #include <bslmf_integralconstant.h> #include <bsls_compilerfeatures.h> #include <bsls_keyword.h> namespace bsl { // ========================== // struct is_lvalue_reference // ========================== template <class t_TYPE> struct is_lvalue_reference : false_type { // This 'struct' template provides a meta-function to determine whether the // (template parameter) 't_TYPE' is a (possibly cv-qualified) lvalue // reference type. This generic default template derives from // 'bsl::false_type'. A template specialization is provided (below) that // derives from 'bsl::true_type'. }; template <class t_TYPE> struct is_lvalue_reference<t_TYPE&> : true_type { // This partial specialization of 'is_lvalue_reference' derives from // 'bsl::true_type' for when the (template parameter) 't_TYPE' is an lvalue // reference type. }; #ifdef BSLS_COMPILERFEATURES_SUPPORT_VARIABLE_TEMPLATES template <class t_TYPE> BSLS_KEYWORD_INLINE_VARIABLE constexpr bool is_lvalue_reference_v = is_lvalue_reference<t_TYPE>::value; // This template variable represents the result value of the // 'bsl::is_lvalue_reference' meta-function. #endif } // 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 ----------------------------------