In C++ •
pointer to function; • pointer to
member function; •
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. import std; struct Foo { void operator()() const { std::println("Called."); } }; int main() { Foo instance; instance(); // This will output "Called." to the screen. }
In C# •
delegate; •
lambda expression.
In PHP PHP 5.3+ has
first-class functions that can be used e.g. as parameter to the usort() function: $a = array(3, 1, 4); usort($a, function ($x, $y) { return $x - $y; }); It is also possible in PHP 5.3+ to make objects invokable by adding a magic __invoke() method to their class: class Minus { public function __invoke($x, $y) { return $x - $y; } } $a = array(3, 1, 4); usort($a, new Minus());
In Python In
Python any object with a __call__() method can be called using function-call syntax. class Foo: def __call__(self) -> None: print("Called.") instance: Foo = Foo() instance() # This will output "Called." to the screen. Another example: class Accumulator: def __init__(self, n: int) -> None: self.n = n def __call__(self, x: int) -> int: self.n += x return self.n
In Dart Callable objects are defined in
Dart using the call() method. class WannabeFunction { call(String a, String b, String c) => '$a $b $c!'; } main() { var wf = new WannabeFunction(); var out = wf("Hi","there,","gang"); print('$out'); }
In Swift In
Swift, callable objects are defined using callAsFunction. struct CallableStruct { var value: Int func callAsFunction(_ number: Int, scale: Int) { print(scale * (number + value)) } } let callable = CallableStruct(value: 100) callable(4, scale: 2) callable.callAsFunction(4, scale: 2) // Both function calls print 208. ==References==