closurize(): Converts any valid PHP callable into a Closure. Requires PHP 5.4.0+.

closurize.php

<?php
/**
 * Converts any valid PHP callable into a Closure. Requires PHP 5.4.0+.
 *
 * The ramifications of this are many, but basically it means that any function
 * or method can be converted into a Closure, bound to another scope, and
 * executed easily. Works properly even with private methods.
 *
 * - On success, returns a Closure corresponding to the provided callable.
 * - If the parameter is not callable, issues an E_USER_WARNING and returns a
 *   Closure which only returns null.
 * - In the event of a strange or unrecoverable situation (e.g. providing a
 *   non-static method without an object), an UnexpectedValueException is
 *   thrown.
 *
 * @author Matthew Lanigan <rintaun@gmail.com>
 * @copyright (c) 2012, Matthew Lanigan
 * @license http://www.opensource.org/licenses/mit-license.php MIT License
 * @link https://gist.github.com/2773168 Official closurize() gist
 * @param callable $callable
 * @return \Closure
 * @throws \UnexpectedValueException
 */
function closurize($callable) {
	if ($callable instanceof \Closure) {
		return $callable;
	}
	$is_callable = function($callable) {
		return \is_callable($callable);
	};
	$error = function() {
		$debug = \debug_backtrace(\DEBUG_BACKTRACE_PROVIDE_OBJECT, 2);
		$fmt = 'Parameter 1 for closurize() must be callable ' .
		       'in %s on line %d (issued at %s on line %d)';
		$error = \sprintf($fmt, $debug[1]['file'], $debug[1]['line'],
		                       $debug[0]['file'], $debug[0]['line']);
		\trigger_error($error, \E_USER_WARNING);
		return function() {
			return null;
		};
	};
	$object = null;
	$class  = null;
	$debug = \debug_backtrace(\DEBUG_BACKTRACE_PROVIDE_OBJECT, 2);
	if (isset($debug[1]['object']) && \is_object($debug[1]['object'])) {
		$object = $debug[1]['object'];
		$class  = $debug[1]['class'];
		$is_callable = $is_callable->bindTo($object, $object);
	}
	if (!$is_callable($callable)) {
		if (isset($callable[0]) && is_object($callable[0])) {
			$is_callable = $is_callable->bindTo($callable[0], $callable[0]);
		} else if (isset($callable[0]) && \class_exists($callable[0])) {
			$is_callable = $is_callable->bindTo(null, $callable[0]);
		}
		if (!$is_callable($callable)) {
			return $error();
		}
	}
	if (\is_string($callable) && (\strpos($callable, '::') === false)) {
		$ref = new \ReflectionFunction($callable);
		return $ref->getClosure();
	} else if (\is_string($callable)) {
		$callable = \explode('::', $callable);
	}
	if (!\is_array($callable)) {
		throw new \UnexpectedValueException('Callable is not string, array, '.
		                                   'or Closure');
	}
	if (\is_object($callable[0])) {
		$ref = new \ReflectionMethod($callable[0], $callable[1]);
		return $ref->getClosure($callable[0]);
	}
	if (!\is_string($callable[0])) {
		throw new \UnexpectedValueException('Callable class is not string ' .
		                                   'or object');
	}
	switch ($callable[0]) {
		case 'self':
			if (!\is_object($object) && \is_null($class)) {
				return $error();
			}
			$self = function() {
				return \get_class();
			};
			$self = $self->bindTo($object, $class);
			$ref = new \ReflectionMethod($self(), $callable[1]);
			$callable[0] = $object;
			break;
		case 'static':
			if (!\is_object($object)) {
				return $error();
			}
			$static = function() {
				return \get_called_class();
			};
			$static = $static->bindTo($object, $class);
			$ref = new \ReflectionMethod($static(), $callable[1]);
			$callable[0] = $object;
			break;
		case 'parent':
			if (!\is_object($object)) {
				return $error();
			}
			$parent = function() {
				return \get_parent_class();
			};
			$parent = $parent->bindTo($object, $class);
			$ref = new \ReflectionMethod($parent(), $callable[1]);
			$callable[0] = $object;
			break;
		default:
			$ref = new \ReflectionMethod($callable[0], $callable[1]);
			break;
	}
	if (!$ref->isStatic() && \is_object($callable[0])) {
		return $ref->getClosure($callable[0]);
	} else if (!$ref->isStatic()) {
		throw new \UnexpectedValueException('Callable method is not static, ' .
		                                   'but no calling object available');
	}
	return $ref->getClosure();
}

Can you give some examples of the input that is allowed in the function?

This seems so pointless! Thanks for the LOL :)

This is not pointless, this will be implemented as Closure::fromCallable() in PHP 7.1 ;)

all those checks and errors are unnecessary.

function closurize ( callable $callable ) {
    if ($callable instanceof \Closure) {
        return $callable;
    }
    return function() use ($callable) {
        return call_user_func_array($callable,func_get_args());
    };
}

@yoosefi no they are not, if you need to bind a new $this to the closure for example, your method won't work as you wrap the function.