FlexibleCallback

FlexibleCallback allows for more flexibility in callback functions.

Specifically, it allows you to:

• Unregister callbacks even if it's not otherwise possible
• Change an already registered callback
• Create callback queues
• Simply return values instead of running a function

So where would I need something like that?

Well, for example register_shutdown_function() won't allow you to unregister or change a callback once it's been registered. FlexibleCallback allows you to circumvent that limitation.

Installation

composer require schlaus/flexiblecallback

...or just download and include FlexibleCallback.php. There are no dependencies, so you're good to go.

Usage

The basics

use Schlaus\FlexibleCallback\FlexibleCallback;

$closure = new FlexibleCallback(function() {
    return "Hello, world!";
});

$closure();     // "Hello, world!"

// register_shutdown_function($closure);

$plainValue = new FlexibleCallback("I'm a return value");

$plainValue();  // "I'm a return value"

$queue = new FlexibleCallback(
    array(
        function() {
            return "Callback 1";
        },
        function() {
            return "Callback 2";
        }
    )
);

$queue();       // "Callback 2"

$queue->unregister();

$queue();       // null

Change a callback afterwards

$callback = new FlexibleCallback("I don't do anything");

$callback->setCallback("I'm much more useful");

$callback();    // "I'm much more useful"

$callback->setCallback(function() {
    return "But I'm the best";
});

$callback();    // "But I'm the best"

// To enforce a callback type there are two handy methods

$callback = new FlexibleCallback;

$callback->setReturnValue("I'm a string")   // Only allows non-callables

$callback->setCallbackFunction(function() { // Only allows callables
    // Awesome things
});

$callback->setCallbackFunction("But I'm not a function!") // InvalidArgumentException

Callback queues

// Create a queue while you're instancing the class...
$queue = new FlexibleCallback(array(
    function() {},
    function() {},
    //...
));
// NOTE: This is a queue, not a stack. First in is first out.

// ... or change an already existing object into a queue
$queue = new FlexibleCallback;
$queue->pushCallbackFunction(function(){});
$queue->pushCallbackFunction(function(){});

// A queue can only contain callables, not values
$queue = new FlexibleCallback("string");
$queue->pushCallbackFunction(function() {
    return "I'm a function";
});

$queue();       // "I'm a function"

Callback arguments in queues

// By default, the same arguments are passed to each callback.
// If a callback in queue returns false, queue execution stops.
// It's possible to change this behaviour so, that instead
// return values are given as the first argument to subsequent
// callbacks.

$queue = new FlexibleCallback;
$queue->includePreviousReturnValue();

$queue = setCallbackFunction(array(
    function($arg1, $arg2) {
        // Since this is the first callback, $arg1 is always null
        // and $arg2 is the first argument passed by the caller
        return false;
    },
    function($arg1, $arg2) {
        // $arg1 is now false, and $arg2 is the same as it was
        // in the previous callback.
    }
));


$queue->excludePreviousReturnValue(); // back to default

Checking what's been loaded

$callback = new FlexibleCallback("Testing!");

$callback->getCallback();   // "Testing!"

$callback->getType();       // "value"

$callback->pushCallbackFunction(function() {
    return "Hello!";
});

$callback->getType();       // "callable"

$function = $callback->getCallback();

$function();                // "Hello!"

$callback->pushCallbackFunction(/*...*/);

$callback->getType();       // "queue"

// $queue will contain all callbacks in queue
$queue = $callback->getCallback();

$callback->setReturnValue(null);

$callback->getType();       // null

$callback->unregister();

$callback->getType();       // null

Converting the queue to a stack (sort of)

$callback->setCallbackFunction(
    array_reverse($callback->getCallback())
);

License

MIT