C++ named requirements: FunctionObject

A FunctionObject type is the type of an object that can be used on the left of the function call operator.

Requirements

The type T satisfies FunctionObject if.

• The type T satisfies std::is_object, and

Given.

• f, a value of type T or const T
• args, suitable argument list, which may be empty

The following expressions must be valid:

Expression	Requirements
f(args)	performs a function call

Notes

Functions and references to functions are not function object types, but can be used where function object types are expected due to function-to-pointer implicit conversion.

Standard library

• All pointers to functions satisfy this requirement.
• All Function objects defined in <functional>
• Some return types of functions of <functional>