bslmf_islvaluereference

Detailed Description

Outline

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

Purpose

Provide a compile-time check for lvalue reference types.

Classes

• bsl::is_lvalue_reference: standard meta-function for lvalue reference types
• bsl::is_lvalue_reference_v: the result value of the meta-function

See also

bslmf_integralconstant

Description

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

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

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

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

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

assert(false == bsl::is_lvalue_reference<int>::value);
assert(true  == bsl::is_lvalue_reference<int&>::value);

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_lvalue_reference_v variable as follows:

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