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In computer programming, a function object [a] is a construct allowing an object to be invoked or called as if it were an ordinary function, usually with the same syntax (a function parameter that can also be a function). In some languages, particularly C++, function objects are often called functors (not related to the functional programming ...
C++ also allows objects to provide an implementation of the function call operation. The Standard Template Library accepts these objects (called functors) as parameters. Many dynamic languages, such as JavaScript, Lua, Python, Perl [1] [2] and PHP, allow a function object to be passed.
C++ includes support for object-oriented programming, so classes can have methods (usually referred to as member functions). Non-static member functions (instance methods) have an implicit parameter (the this pointer) which is the pointer to the object it is operating on, so the type of the object must be included as part of the type of the ...
functor; lambda expression. std::function is a template class that can hold any callable object that matches its signature. In C++, any class that overloads the function call operator operator() may be called using function-call syntax.
Manipulation of these parameters can be done by using the routines in the standard library header < stdarg. h >. In C++, the return type can also follow the parameter list, which is referred to as a trailing return type. The difference is only syntactic; in either case, the resulting signature is identical:
takes one or more functions as arguments (i.e. a procedural parameter, which is a parameter of a procedure that is itself a procedure), returns a function or value as its result. All other functions are first-order functions. In mathematics higher-order functions are also termed operators or functionals.
Both expressions have the same meaning and behave in exactly the same way. The latter form was introduced to avoid confusion, [3] since a type parameter need not be a class until C++20. (It can be a basic type such as int or double.) For example, the C++ Standard Library contains the function template max(x, y) which returns the larger of x and ...
As is the case in all instances of currying, the formula above describes an adjoint pair of functors: for every fixed set , the functor is left adjoint to the functor . In the category of sets , the object Y X {\displaystyle Y^{X}} is called the exponential object .