PHP依赖注入实现

class Bim
{
    public function doSomething()
    {
        echo __METHOD__, '|';
    }
}

class Bar
{
    private $bim;

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

    public function doSomething()
    {
        $this->bim->doSomething();
        echo __METHOD__, '|';
    }
}

class Foo
{
    private $bar;

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

    public function doSomething()
    {
        $this->bar->doSomething();
        echo __METHOD__;
    }
}

class Container
{
    private $s = array();

    public function __set($k, $c)
    {
        $this->s[$k] = $c;
    }

    public function __get($k)
    {
        // return $this->s[$k]($this);
        return $this->build($this->s[$k]);
    }

    /**
     * 自动绑定(Autowiring)自动解析(Automatic Resolution)
     *
     * @param string $className
     * @return object
     * @throws Exception
     */
    public function build($className)
    {
        // 如果是匿名函数(Anonymous functions),也叫闭包函数(closures)
        if ($className instanceof Closure) {
            // 执行闭包函数,并将结果
            return $className($this);
        }

        /** @var ReflectionClass $reflector */
        $reflector = new ReflectionClass($className);

        // 检查类是否可实例化, 排除抽象类abstract和对象接口interface
        if (!$reflector->isInstantiable()) {
            throw new Exception("Can't instantiate this.");
        }

        /** @var ReflectionMethod $constructor 获取类的构造函数 */
        $constructor = $reflector->getConstructor();

        // 若无构造函数,直接实例化并返回
        if (is_null($constructor)) {
            return new $className;
        }

        // 取构造函数参数,通过 ReflectionParameter 数组返回参数列表
        $parameters = $constructor->getParameters();

        // 递归解析构造函数的参数
        $dependencies = $this->getDependencies($parameters);

        // 创建一个类的新实例,给出的参数将传递到类的构造函数。
        return $reflector->newInstanceArgs($dependencies);
    }

    /**
     * @param array $parameters
     * @return array
     * @throws Exception
     */
    public function getDependencies($parameters)
    {
        $dependencies = [];

        /** @var ReflectionParameter $parameter */
        foreach ($parameters as $parameter) {
            /** @var ReflectionClass $dependency */
            $dependency = $parameter->getClass();

            if (is_null($dependency)) {
                // 是变量,有默认值则设置默认值
                $dependencies[] = $this->resolveNonClass($parameter);
            } else {
                // 是一个类,递归解析
                $dependencies[] = $this->build($dependency->name);
            }
        }

        return $dependencies;
    }

    /**
     * @param ReflectionParameter $parameter
     * @return mixed
     * @throws Exception
     */
    public function resolveNonClass($parameter)
    {
        // 有默认值则返回默认值
        if ($parameter->isDefaultValueAvailable()) {
            return $parameter->getDefaultValue();
        }

        throw new Exception('I have no idea what to do here.');
    }
}


$c = new Container();
$c->foo = 'foo';
$foo = $c->foo;
$foo->doSomething();

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