Callable object

A callable object, in computer programming, is any object that can be called like a function.

In different languages

In C++

• pointer to function;
• pointer to member function;
• functor;
• lambda expression.
• <code>std::function</code> is a template class that can hold any callable object that matches its signature.

In C++, any class that overloads the function call operator <code>operator()</code> may be called using function-call syntax.

In C#

• delegate;
• lambda expression.

In PHP

PHP 5.3+ has first-class functions that can be used e.g. as parameter to the <code>usort()</code> function:

It is also possible in PHP 5.3+ to make objects invokable by adding a magic <code>__invoke()</code> method to their class:

In Python

In Python any object with a <code>__call__()</code> method can be called using function-call syntax.

Another example:

In Dart

Callable objects are defined in Dart using the <code>call()</code> method.

In Swift

In Swift, callable objects are defined using <code>callAsFunction</code>.

References

External links

• C++ Callable concept