What does 'this followed by square brackets' mean in PHP?

Question

I found one code block in Laravel like below:

/**
 * Register a "before" application filter.
 *
 * @param  \Closure|string  $callback
 * @return void
 */
public function before($callback)
{
    return $this['router']->before($callback);
}

What does $this['router'] mean at here? Can anyone explain the $this['xx'] form? Is it an array?

The class probably implements `ArrayAccess` (http://php.net/manual/en/class.arrayaccess.php) — naththedeveloper, Aug 15 '17 at 14:19
Here's an example which demonstrates the behaviour: https://3v4l.org/Q2Lhi — naththedeveloper, Aug 15 '17 at 14:25
Yeah! You are right! I'm just looking for what you said. Thank you very much! @naththedeveloper — Rex Tsao, Aug 15 '17 at 14:34

score 5 · Accepted Answer · answered Aug 15 '17 at 14:28

The fact that your variable is called $this means that it can't be an ordinary array - that variable name is reserved for the current instance of a class.

Using square brackets to access an object is a sign that the class implements that ArrayAccess interface - that is, it can be accessed using the operators normally reserved for basic arrays.

Retrieving a value from a class that implements ArrayAccess using square bracket notation invokes the class's offsetGet method, with the provided key as the $offset argument. The most common use is to allow access to a class's member variables, but the class itself can choose to perform any action in this method.

In your case, I think you're looking at the Laravel application class, which will result in the router item being returned from the dependency injection container.

score 2 · Answer 2 · answered Aug 15 '17 at 14:26

$this['router'] references to router service in laravel service container. A service container (or dependency injection container) is simply a PHP object that manages the instantiation of services (i.e. objects).

see : What is the concept of Service Container in Laravel?

score 1 · Answer 3 · answered Aug 15 '17 at 14:18

It simply means that it is an array. You use the square brackets, with a key (which can be a name (string, wrapped in quotes), or a number) to identify the proper value from the array.

In your code, $this['router'] refers to an array that contained in the class you are looking at, and that is the identifier to select what it needs, router being the key.

What does 'this followed by square brackets' mean in PHP?

3 Answers3