laravel如何在Facade类中使用object作为数组

Question

I've noted that for creating a facade class, laravel provides only name "db"

framework/src/Illuminate/Support/Facades/DB.php

class DB extends Facade
{
    /**
     * Get the registered name of the component.
     *
     * @return string
     */
    protected static function getFacadeAccessor()
    {
        return 'db';
    }
}

I looked deeper and figured out that this method uses the provided name

framework/src/Illuminate/Support/Facades/Facade.php

protected static function resolveFacadeInstance($name)
{
    if (is_object($name)) {
        return $name;
    }
    if (isset(static::$resolvedInstance[$name])) {
        return static::$resolvedInstance[$name];
    }
    return static::$resolvedInstance[$name] = static::$app[$name];
}

I understand first and second If statements.

But I have problems with understanding this:

return static::$resolvedInstance[$name] = static::$app[$name]

As I understood that $app is a protected property of Facade class which contains an instance of \\Illuminate\\Contracts\\Foundation\\Application class.

/**
     * The application instance being facaded.
     *
     * @var \Illuminate\Contracts\Foundation\Application
     */
    protected static $app;

My two questions:

How is it possible to use an object as an array( static::$app[$name] ) if Application class doesn't extends ArrayObject class?

How laravel understands which class to call with providing only a short name 'db'?

Answer 1

Clicking through the Laravel source, I found this. As you can see, ApplicationContract (the private static $app from your question) is implemented by Application . This is in turn derived from Container , which implements the PHP core ArrayAccess interface. Carefully implementing this whole chain eventually makes Applicatin accessible like an array.

Turns out it boils down to good ole' object oriented programming :)

// Illuminate/Foundation/Application.php
class Application extends Container implements ApplicationContract, HttpKernelInterface
                          ^^^^^^^^^            ^-> the private static $app in your question.

// Illuminate/Container/Container.php
class Container implements ArrayAccess, ContainerContract
                           ^^^^^^^^^^^

// PHP core ArrayAccess documentation
/**
 * Interface to provide accessing objects as arrays.
 * @link http://php.net/manual/en/class.arrayaccess.php
 */
interface ArrayAccess {

Answer 2

You can look this, php manual and use ArrayAccess interface:

http://php.net/manual/en/class.arrayaccess.php