How to reference this in closure - php

Question

I am using PHP Version 7.1.1.
In index.php of my MVC I create a route collection ($routes). To it I want to add a route group (with addGroup). This addition process relies on a closure (e.g. an anonymous function), passed as argument to addGroup. Inside of closure I am trying to reference the collection with $this, so that I can add one or more routes to it (with addRoute, a method of the collection).
Unfortunately I could not achieve that, although I made some tries. I miss a piece of the closures theory, somewhere. I would appreciate, if you would provide me an advice.
The "problem" is, that, in order to achieve a simplified usability for the user, I am trying to avoid the direct use of a closure parameter. Why? Because inside addGroup I am already in the collection's scope and from there I am calling the closure. This way I can pass the collection's instance ($this) as argument to the executeGroupHandler method and, therefore to executeGroupHandler as well.
Thank you for your time and patience!
index.php
$routes = new RouteCollection();
$routes->addGroup('/test', function() {
$this->addRoute('GET', '/group', function() {
echo 'Hello from route /test/group';
});
});
RouteCollection
class RouteCollection implements CollectionInterface {
public function addGroup(string $groupPattern, callable $groupHandler) {
$group = new RouteGroup($groupPattern, $groupHandler);
return $group->executeGroupHandler($this);
}
public function addRoute($httpMethod, string $routePattern, $routeHandler) {
//...
return $this;
}
}
RouteGroup
class RouteGroup {
private $groupPattern;
private $groupHandler;
public function __construct(string $groupPattern, callable $groupHandler) {
$this->groupPattern = $groupPattern;
$this->groupHandler = $groupHandler;
}
public function executeGroupHandler(CollectionInterface $routeCollection) {
return call_user_func_array($this->groupHandler, [$routeCollection]);
}
}

Answer 1

Try this:
$routes->addGroup('/test', function() use ($routes) {
$routes->addRoute('GET', '/group', function() {
echo 'Hello from route /test/group';
});
});
You are trying to access $this or $routes from a closure that is outside the scope of the class

Answer 2

In an abstract sense you can achieve this using the bind function of a closure:
$routes = new RouteCollection();
$routeHandler = Closure::bind(function() {
$this->addRoute('GET', '/group', function() {
echo 'Hello from route /test/group';
});
}, $routes);
$routes->addGroup('/test', $routeHandler);
This is useful when you want to pass this closure around but want to maintain scope.

Answer 3

I decided to present the solution in this post, as accepted answer, only to provide a compact overview of it, together with its implementation. But:
Credits:
The solution that elegantly fulfills all my requirements, and that I have chosen to use, was kindly presented by #apokryfos. The idea proposed by #ArtisticPhoenix was very correct as well.
Thank you very much guys! I appreciate your help.
Solution:
The idea is, that, if you bind the closure to an object - in my case the collection ($routes), then the object is accessible within the scope of the closure and can be referenced with $this.
Based on this idea I could achieve an implementation which not only allows the user to not pass any arguments to the group handler callback (the closure function), but also to still pass arguments (the container object $routes) if he wishes it.
Implementation of the solution:
index.php
$routes = new RouteCollection();
$routes
// The most simple and elegant use-case.
->addGroup('/group1', function() {
$this->addRoute('GET', '/route1', function() {
echo 'Hello from route /group1/route1';
});
})
// An optional use-case.
->addGroup('/group2', function($routes) {
$routes->addRoute('GET', '/route1', function() {
echo 'Hello from route /group2/route1';
});
})
// Another optional use-case.
->addGroup('/group3', function() use ($routes) {
$routes->addRoute('GET', '/route1', function() {
echo 'Hello from route /group3/route1';
});
})
;
RouteCollection
class RouteCollection implements CollectionInterface {
public function addGroup(string $groupPattern, callable $groupHandler) {
if ($groupHandler instanceof Closure) {
$groupHandler = $groupHandler->bindTo($this);
}
$group = new RouteGroup($groupPattern, $groupHandler);
$group->executeGroupHandler($this);
return $this;
}
}
RouteGroup
class RouteGroup {
public function executeGroupHandler(CollectionInterface $routeCollection) {
return call_user_func_array($this->groupHandler, [$routeCollection]);
}
}