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: 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