Component bslmf_isrvaluereference [Package bslmf]

Provide a compile-time check for rvalue reference types. More...

Classes
struct	bsl::is_rvalue_reference< t_TYPE >

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Detailed Description

Outline

• Purpose
• Classes
• Description
  • Usage
    • Example 1: Verify Rvalue Reference Types

Purpose:

Provide a compile-time check for rvalue reference types.

Classes:

bsl::is_rvalue_reference	standard meta-function for rvalue reference types
bsl::is_rvalue_reference_v	the result value of the standard meta-function

See also:

Component bslmf_integralconstant

Description:

This component defines a meta-function, bsl::is_rvalue_reference and a template variable bsl::is_rvalue_reference_v, that represents the result value of the bsl::is_rvalue_reference meta-function, that may be used to query whether a type is an rvalue reference type.

bsl::is_rvalue_reference meets the requirements of the is_rvalue_reference template defined in the C++11 standard [meta.unary.cat].

Note that the template variable is_rvalue_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_rvalue_reference_v is defined as an inline constexpr bool variable. Otherwise, if the compiler supports the variable templates C++14 compiler feature, bsl::is_rvalue_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 Rvalue Reference Types:

Suppose that we want to assert whether a set of types are rvalue reference types.

Now, we instantiate the bsl::is_rvalue_reference template for both a non-reference type and an rvalue reference type, and assert the value static data member of each instantiation:

  assert(false == bsl::is_rvalue_reference<int>::value);
#if defined(BSLS_COMPILERFEATURES_SUPPORT_RVALUE_REFERENCES)
  assert(true  == bsl::is_rvalue_reference<int&&>::value);
#endif

Note that rvalue reference is a feature introduced in the C++11 standard, and may not be supported by all compilers.

Also 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_rvalue_reference_v variable as follows:

#ifdef BSLS_COMPILERFEATURES_SUPPORT_VARIABLE_TEMPLATES
  assert(false == bsl::is_rvalue_reference_v<int>);
  assert(true  == bsl::is_rvalue_reference_v<int&&>);
#endif