C++ concepts: FunctionObject

 

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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.

In addition, the following standard library facilities require a FunctionObject which isn't Callable, Hash, or Predicate type.

std::unique_ptr