<?php

/**

*Internal Functions

*/

$callback = 'myFunction';

usort($array, $callback);

/*

You can also use arrays to denote object or static class method calls:

Listing 10.8: Using arrays ti soecify callbacks

*/

//objet method call

$callback = [$obj, 'method']; // $obj->method()

usort($array, $callback);

//or static method

$callback = ['SomeClass','method']; //SomeClass::method()

usort($array, $callback);

/*

Using a class as a callback

*/

class Sorter{

public function __invoke($a, $b){

//sort

}

}

$sorter = new Sorter();

usort($sorter);

/*

Userland Function

Variable functions

*/

$callback = 'myFunction';

$callback();

//object method call;

$callback = [$obj, 'method']; //$obj->method() callbak

$callback();

//static method ;

$callback = ['SomeClass', 'method']; //SomeClass::method() callbak

$callback();

//closures

$callback = function(){};

$callback();

class invokeCallback{

public function __invoke($a, $b){

//sort

}

}

$callback = new invokeCallback();

$callback();