php闭包使用例子

一.依据闭包实现一个容器

class Di
{
    private $factory;

    public function set($id, $value)
    {
        $this->factory[$id] = $value;
    }

    public function get($id)
    {
        $val = $this->factory[$id];
        return $val();//如果不加括号,仅仅返回的是闭包类,并不是User实例
    }
}

class User
{
    private $username;

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

    public function getUserName()
    {
        return $this->username;
    }
}

$di = new Di();

// 在此使用了闭包,所以实际上并不会实例化User类,只有在后面get的时候才会实例化
$di->set('a', function(){
    return new User('张三');
});

var_dump($di->get('a')->getUserName());

　　

二.使用闭包作为回调

class Cart
{
    CONST PRICE_BUTTER = 1.0;
    CONST PRICE_MILK = 5.05;

    protected $products = [];

    public function add($product, $quantity)
    {
        $this->products[$product] = $quantity;
    }

    public function getQuantity($product)
    {
        return isset($this->products[$product]) ? $this->products[$product]: false;
    }

    public function getTotal($tax)
    {
        $total = 0.00;
        $callback = function($quantity, $product) use ($tax, &$total) {
            $priceItem = constant(__CLASS__ . '::PRICE_' . strtoupper($product));
            $total += ($priceItem * $quantity) * ($tax + 1.0);
        };

        array_walk($this->products, $callback);
        return round($total, 2);
    }
}

$cart = new Cart();
$cart->add('butter', 1);
$cart->add('milk', 5);

echo $cart->getTotal(0.05);

　　

三.使用闭包函数调用类中方法

class Grid
{
    protected $builder;
    protected $attribute;

    public function __construct(Closure $builler)
    {
        $this->builder = $builler;
    }

    public function addColumn($name, $value)
    {
        $this->attribute[$name] = $value;
        return $this;
    }

    public function build()
    {
        // 这儿回调闭包函数,参数为this
        call_user_func($this->builder, $this);
    }

    public function __toString()
    {
        $this->build();

        $str = '';
        $call = function($val, $key) use(&$str) {
             $str .= "$key=>$val;";
        };
        array_walk($this->attribute, $call);

        return $str;
    }
}

$grid = new Grid(
    // 传入闭包函数,带参数
    function($grid) {
        $grid->addColumn('key1', 'val1');
        $grid->addColumn('key2', 'val2');
    }
);

echo $grid;

　　

闭包在对象中的一个典型使用场景就是留出一个方法给调用者,让调用者自主决定或组装数据.
如下例:让调用者决定如何组装或显示info.

class CalledClass {
    private $name;
    private $age;
    private $info;

    public function __construct($name, $age, Closure $callable)
    {
        $this->name = $name;
        $this->age = $age;
        call_user_func($callable, $this);
        // 这相当于
        // $callable($this);
    }

    public function setInfo($info)
    {
        $this->info = $info;
    }

    public function getInfo()
    {
        echo $this->info;
    }

    /**
     * @return mixed
     */
    public function getName()
    {
        return $this->name;
    }

    /**
     * @return mixed
     */
    public function getAge()
    {
        return $this->age;
    }

}

$c = new CalledClass('php', 10, function (CalledClass $c) {
    echo $c->getAge() . $c->getName();
    $c->setInfo($c->getAge() . $c->getName());
});

echo $c->getInfo();