php reflection api example

reflection-api.php

<?php 

class User {

    protected $name;

    public function __construct($name)
    {
        $this->name = $name;
    }
}

interface UserRepositoryInterface {}

class EloquentUserRepository implements UserRepositoryInterface {

    protected $user;

    public function __construct(User $user)
    {
        $this->user = $user;
    }
}

class UsersController {

    protected $userRepository;

    public function __construct(UserRepositoryInterface $userRepository)
    {
        $this->userRepository = $userRepository;
    }
}

class Container {

    protected $bindings = [];

    public function bind($interface, $implementation)
    {
        $this->bindings[$interface] = $implementation;
    }

    public function resolve($className)
    {
        $reflectionClass = new ReflectionClass($className);

        $constructor = $reflectionClass->getConstructor();

        if (is_null($constructor)) return new $className;

        $params = $constructor->getParameters();

        if (count($params) === 0) return new $className;

        $newInstanceParams = [];

        foreach ($params as $param)
        {
            if ( ! is_null($param->getClass()))
            {
                $dependency = $param->getClass();
                $dependencyName = $dependency->getName();

                if (isset($this->bindings[$dependencyName]))
                {
                    $dependencyName = $this->bindings[$dependencyName];
                    
                    if ( ! is_string($dependencyName)) // find out if binded value is closure
                    {
                        return $reflectionClass->newInstance($dependencyName());
                    }
                }

                $newInstanceParams[] = $this->resolve($dependencyName);
            }
        }
        return $reflectionClass->newInstanceArgs($newInstanceParams);
    }
}

$container = new Container;
$container->bind('UserRepositoryInterface', 'EloquentUserRepository');
$container->bind('User', function() {
    return new User('Jernej');
});

var_dump($container->resolve('UsersController'));