PHP/function variable

About

A variable can store a reference to a function, which can then be called from the variable.

Named Functions/Methods

The thing that isn't explained very well in the documentation is that if you want to assign a predefined function to a variable, you just use a string which is a callable/accessible form of the function.

function Example1() { echo "Example1 was called!\n"; }

#$fEx1 = Example1;  // does not work; sees "Example1" as a constant
$fEx1 = 'Example1';

$fEx1();  // prints "Example1 was called!"

class cExample2 {
    static public function Test1() { echo "Test1 was called!\n"; }
}

#$fEx2 = cExample2::Test1;  // does not work; sees "Test1" as a class constant
$fEx2 = 'cExample2::Test1';
$fEx2(); // prints "Test1 was called!"

The variable can be used to call the function in exactly the same way as if it had been assigned an anonymous function.

Anonymous Functions

$fEx3 = function() { echo "Anonymous function was called!\n"; };
$fEx3();  // prints "Anonymous function was called!"

Unlike with predefined functions, however, the type for the variable is Callable rather than string.

Documentation

• Language Reference:
  • Types:
    • Callbacks / Callables
  • Functions:
    • Anonymous functions
    • Variable functions
    • Function arguments
• Function Reference:
  • Variable and Type Related Extensions:
    • Function Handling:
      • Function handling Functions:
        • call_user_func()