Component bslmf_addrvaluereference [Package bslmf]

Provide a compile-time type transformation to rvalue reference. More...

Outline

• Purpose
• Classes
• Description
  • Usage
    • Example 1: Transform to Rvalue Reference Types

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:

Component bslmf_integralconstant, Component 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.