Component bslmf_isfunction [Package bslmf]

Provide a compile-time check for determining function types. More...

Outline

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

Purpose:

Provide a compile-time check for determining function types.

Classes:

bsl::is_function	standard meta-function for determining function types
bsl::is_function_v	the result value of bsl::is_function

See also:

Component bslmf_integralconstant

Description:

This component defines a meta-function, bsl::is_function and a template variable bsl::is_function_v, that represents the result value of the bsl::is_function meta-function, that may be used to query whether a template parameter type is a function type.

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

Note that the template variable is_function_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_function_v is defined as an inline constexpr bool variable. Otherwise, if the compiler supports the variable templates C++14 compiler feature, bsl::is_function_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 Function Types:

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

Now, we instantiate the bsl::is_function template for both a non-function type and a function type, and assert the value static data member of each instantiation:

  assert(false == bsl::is_function<int>::value);
  assert(true  == bsl::is_function<int (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_function_v variable as follows:

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