Component bslmf_isreference [Package bslmf]

Provide a meta-function to test reference types. More...

Classes
struct	bsl::is_reference< t_TYPE >
struct	bsl::is_reference< t_TYPE & >

---

Detailed Description

Outline

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

Purpose:

Provide a meta-function to test reference types.

Classes:

bsl::is_reference	standard meta-function for testing reference types
bsl::is_reference_v	the result value of the standard meta-function

See also:

Description:

This component defines a meta-function, bsl::is_reference and a template variable bsl::is_reference_v, that represents the result value of the bsl::is_class meta-function, that may be used to query whether a type is an (lvalue or rvalue) reference type.

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

Note that the template variable is_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_reference_v is defined as an inline constexpr bool variable. Otherwise, if the compiler supports the variable templates C++14 compiler feature, bsl::is_reference_v is defined as a non-'const' 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 Reference Types:

Suppose that we want to assert whether a set of types are (lvalue or rvalue) reference types.

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

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

Note that rvalue reference is a feature introduced in the C++11 standand, 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_reference_v variable as follows:

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