A callable object, in

computer programming Computer programming is the process of performing a particular computation (or more generally, accomplishing a specific computing result), usually by designing and building an executable computer program. Programming involves tasks such as anal ...

, is any object that can be called like a

function Function or functionality may refer to: Computing * Function key, a type of key on computer keyboards * Function model, a structured representation of processes in a system * Function object or functor or functionoid, a concept of object-oriente ...

In different languages

In C++

* pointer to function; * pointer to

member function A method in object-oriented programming (OOP) is a procedure associated with a message and an object. An object consists of ''state data'' and ''behavior''; these compose an ''interface'', which specifies how the object may be utilized by any of ...

; *

functor In mathematics, specifically category theory, a functor is a mapping between categories. Functors were first considered in algebraic topology, where algebraic objects (such as the fundamental group) are associated to topological spaces, and m ...

; * 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. #include struct Foo ; int main()

In C#

delegate Delegate or delegates may refer to: * Delegate, New South Wales, a town in Australia * Delegate (CLI), a computer programming technique * Delegate (American politics), a representative in any of various political organizations * Delegate (Unit ...

; * lambda expression.

In PHP

PHP PHP is a general-purpose scripting language geared toward web development. It was originally created by Danish-Canadian programmer Rasmus Lerdorf in 1993 and released in 1995. The PHP reference implementation is now produced by The PHP Group. ...

5.3+ has

first-class function In computer science, a programming language is said to have first-class functions if it treats functions as first-class citizens. This means the language supports passing functions as arguments to other functions, returning them as the values from ...

s that can be used e.g. as parameter to the usort() function: $a = array(3, 1, 4); usort($a, function ($x, $y) ); It is also possible in PHP 5.3+ to make objects invokable by adding a magic __invoke() method to their class:PHP Documentation on Magic Methods
/ref> class Minus $a = array(3, 1, 4); usort($a, new Minus());

In Python

Python Python may refer to: Snakes * Pythonidae, a family of nonvenomous snakes found in Africa, Asia, and Australia ** ''Python'' (genus), a genus of Pythonidae found in Africa and Asia * Python (mythology), a mythical serpent Computing * Python (pro ...

any object with a __call__() method can be called using function-call syntax. class Foo: def __call__(self): print("Called.") foo_instance = Foo() foo_instance() # This will output "Called." to the screen. Another example: class Accumulator: def __init__(self, n): self.n = n def __call__(self, x): self.n += x return self.n

In Dart

Callable objects are defined in Dart using the call() method. class WannabeFunction main()

In Swift

Swift Swift or SWIFT most commonly refers to: * SWIFT, an international organization facilitating transactions between banks ** SWIFT code * Swift (programming language) * Swift (bird), a family of birds It may also refer to: Organizations * SWIFT, ...

, callable objects are defined using callAsFunction. struct CallableStruct let callable = CallableStruct(value: 100) callable(4, scale: 2) callable.callAsFunction(4, scale: 2) // Both function calls print 208.

References

External links

C++ Callable concept
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