Closures in PHP… what, precisely, are they and when would you need to use them?

Question

So I\'m programming along in a nice, up to date, object oriented fashion. I regularly make use of the various aspects of OOP that PHP implements but I am wondering when might I

Answer 1

I like the context provided by troelskn's post. When I want to do something like Dan Udey's example in PHP, i use the OO Strategy Pattern. In my opinion, this is much better than introducing a new global function whose behavior is determined at runtime.

http://en.wikipedia.org/wiki/Strategy_pattern

You can also call functions and methods using a variable holding the method name in PHP, which is great. so another take on Dan's example would be something like this:

class ConfigurableEncoder{
        private $algorithm = 'multiply';  //default is multiply

        public function encode($x){
                return call_user_func(array($this,$this->algorithm),$x);
        }

        public function multiply($x){
                return $x * 5;
        }

        public function add($x){
                return $x + 5;
        }

        public function setAlgorithm($algName){
                switch(strtolower($algName)){
                        case 'add':
                                $this->algorithm = 'add';
                                break;
                        case 'multiply':        //fall through
                        default:                //default is multiply
                                $this->algorithm = 'multiply';
                                break;
                }
        }
}

$raw = 5;
$encoder = new ConfigurableEncoder();                           // set to multiply
echo "raw: $raw\n";                                             // 5
echo "multiply: " . $encoder->encode($raw) . "\n";              // 25
$encoder->setAlgorithm('add');
echo "add: " . $encoder->encode($raw) . "\n";                   // 10

of course, if you want it to be available everywhere, you could just make everything static...