// bslmf_addrvaluereference.h -*-C++-*- #ifndef INCLUDED_BSLMF_ADDRVALUEREFERENCE #define INCLUDED_BSLMF_ADDRVALUEREFERENCE #include <bsls_ident.h> BSLS_IDENT("$Id: $") //@PURPOSE: Provide a compile-time type transformation to rvalue reference. // //@CLASSES: // bsl::add_rvalue_reference: standard meta-function for transforming types // bsl::add_rvalue_reference_t: alias to the return type of the meta-function // //@SEE_ALSO: bslmf_integralconstant, bslmf_addlvaluereference // //@DESCRIPTION: This component defines a meta-function, // 'bsl::add_rvalue_reference', that may be used to transform a type to its // rvalue reference type. // // 'bsl::add_rvalue_reference' and 'bsl::add_rvalue_reference_t' meet the // requirements of the 'add_rvalue_reference' template defined in the C++11 // standard [meta.trans.ref]. // ///Usage ///----- // In this section we show intended use of this component. // ///Example 1: Transform to Rvalue Reference Types /// - - - - - - - - - - - - - - - - - - - - - - - // Suppose that we want to transform some types to rvalue reference types. // // Now, for a set of types, we transform each type to the corresponding rvalue // reference of that type using 'bsl::add_rvalue_reference' and verify the // result: //.. //#if defined(BSLS_COMPILERFEATURES_SUPPORT_RVALUE_REFERENCES) // assert(true == // (bsl::is_same<bsl::add_rvalue_reference<int>::type, int&&>::value)); // assert(false == // (bsl::is_same<bsl::add_rvalue_reference<int>::type, int >::value)); // assert(true == // (bsl::is_same<bsl::add_rvalue_reference<int&>::type, int& >::value)); // assert(true == // (bsl::is_same<bsl::add_rvalue_reference<int&&>::type, int&&>::value)); //.. // Finally, if the current compiler supports alias templates C++11 feature, we // instantiate the 'bsl::add_rvalue_reference_t' template for the same set of // types, and use the 'bsl::is_same' meta-function to assert the resultant type // of each instantiation: //.. //#ifdef BSLS_COMPILERFEATURES_SUPPORT_ALIAS_TEMPLATES // assert(true == // (bsl::is_same<bsl::add_rvalue_reference_t<int>, int&&>::value)); // assert(false == // (bsl::is_same<bsl::add_rvalue_reference_t<int>, int >::value)); // assert(true == // (bsl::is_same<bsl::add_rvalue_reference_t<int&>, int& >::value)); // assert(true == // (bsl::is_same<bsl::add_rvalue_reference_t<int&&>, int&&>::value)); //#endif //#endif //.. // Note that rvalue reference was introduced in C++11 and may not be supported // by all compilers. Note also that according to 'reference collapsing' // semantics [8.3.2], 'add_rvalue_reference' does not transform 't_TYPE' to // rvalue reference type if 't_TYPE' is an lvalue reference type. // // Also note that the 'bsl::add_rvalue_reference_t' avoids the '::type' suffix // and 'typename' prefix when we want to use the result of // 'bsl::add_rvalue_reference' meta-function in templates. #include <bslscm_version.h> #include <bsls_compilerfeatures.h> namespace bsl { #if defined(BSLS_COMPILERFEATURES_SUPPORT_RVALUE_REFERENCES) template <class t_TYPE> struct add_rvalue_reference { // This 'struct' template implements a meta-function to transform the // (template parameter) 't_TYPE' to its rvalue reference type. // PUBLIC TYPES typedef t_TYPE&& type; // This 'typedef' is an alias to the return type of this meta-function. }; template <> struct add_rvalue_reference<void> { // This partial specialization of 'add_rvalue_reference' defines the return // type when it is instantiated with the 'void' type. // PUBLIC TYPES typedef void type; // This 'typedef' is an alias to the return type of this meta-function. }; template <> struct add_rvalue_reference<void const> { // This partial specialization of 'add_rvalue_reference' defines the return // type when it is instantiated with the 'void const' type. // PUBLIC TYPES typedef void const type; // This 'typedef' is an alias to the return type of this meta-function. }; template <> struct add_rvalue_reference<void volatile> { // This partial specialization of 'add_rvalue_reference' defines the return // type when it is instantiated with the 'void volatile' type. // PUBLIC TYPES typedef void volatile type; // This 'typedef' is an alias to the return type of this meta-function. }; template <> struct add_rvalue_reference<void const volatile> { // This partial specialization of 'add_rvalue_reference' defines the return // type when it is instantiated with the 'void const volatile' type. // PUBLIC TYPES typedef void const volatile type; // This 'typedef' is an alias to the return type of this meta-function. }; #ifdef BSLS_COMPILERFEATURES_SUPPORT_ALIAS_TEMPLATES // ALIASES template <class t_TYPE> using add_rvalue_reference_t = typename add_rvalue_reference<t_TYPE>::type; // 'add_rvalue_reference_t' is an alias to the return type of // 'add_rvalue_reference' meta-function. Note, that the 'add_const_t' // avoids the '::type' suffix and 'typename' prefix when we want to use the // result of the meta-function in templates. #endif // BSLS_COMPILERFEATURES_SUPPORT_ALIAS_TEMPLATES #endif // BSLS_COMPILERFEATURES_SUPPORT_RVALUE_REFERENCES } // 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 ----------------------------------