Demo Dependency injection

di.php

<?php

/**
 * Class Dependency injection
 */
class DI
{

    protected $store = [];

    public function register($abstruct, $value)
    {
        $this->store[$abstruct] = $value;
    }

    public function invoke($method, ...$args)
    {
        if (strpos($method, '@') === false) {
            throw new Exception('Argument 1 missing character @');
        }

        $segements = explode('@', $method, 2);
        list($class, $method) = $segements;

        $object = null;
        if ($this->exists($class)) {
            $object = $this->getValue($class);
        } else {
            $object = new $class();
        }

        $ref = new ReflectionClass($object);

        $method = $ref->getMethod($method);
        if (!$method) {
            throw new Exception("{$class} without method named {$method}");
        }

        $params = [];
        foreach ($method->getParameters() as $value) {
            $type = $value->getType();
            if ($type) {
                $typeName = $type->getName();
                if ($this->exists($typeName)) {
                    $params[] = $this->getValue($typeName);
                } elseif ($value->allowsNull()) {
                    $params[] = $value->getDefaultValue();
                } else {
                    $params[] = new $typeName();
                }
            } elseif ($value->allowsNull()) {
                $params[] = $value->getDefaultValue();
            } else {
                throw new Exception("{$value->getName()} has no matched");
            }
        }

        foreach ($args as $arg) {
            $params[] = $arg;
        }

        return $method->invokeArgs($object, $params);
    }

    /**
     * @param $abstruct
     * @return mixed|null
     */
    public function getValue($abstruct)
    {
        $value = $this->store[$abstruct] ?? null;

        return $value instanceof Closure ? $value() : $value;
    }

    /**
     * @param $abstruct
     * @return bool
     */
    public function exists($abstruct)
    {
        return isset($this->store[$abstruct]);
    }

}

class UserModel
{
    private $name;

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

    public function getName()
    {
        return $this->name;
    }
}

class OrderModel
{
    public function description()
    {
        return "I'm order model.";
    }
}

$di = new DI();
$di->register(UserModel::class, function () {
    return new UserModel("WatchDog");
});

// 不提前注册，尝试自动实例化
//$di->register(OrderModel::class, function () {
//    return new OrderModel();
//});

class Controller
{
    /**
     * @param OrderModel $order 依赖订单模型（自动处理）
     * @param UserModel $user   依赖用户模型（获取提前注册的对象）
     * @param array $options    配置
     * @return string
     */
    public function index(OrderModel $order, UserModel $user, $options = ['key' => 'value'])
    {
        return sprintf("%s: %s\nOptions: %s", $user->getName(), $order->description(), serialize($options));
    }
}

$result = $di->invoke('Controller@index');
echo $result . PHP_EOL;

Test

→ php di.php
WatchDog: I'm order model.
Options: a:1:{s:3:"key";s:5:"value";}