Php 闭包绑定$This和垃圾收集器

您几乎不可能有一个简单的接口，它期望存在一个run()方法.由此，您可以使用$this上下文来调用它.每个$strategy实例都有自己的$this作用域.

演示:https://3v4l.org/eCtZU

interface StrategyInterface {
    public function run();
}

class Strategy implements StrategyInterface
{
    protected ?string $value = null;
    public function __construct(private Closure $closure)
    {
        $this->value = (string) rand(1, 100);
    }

    public function run()
    {
        $this->closure->call($this);
    }
}

for ($i = 0; $i < 10; ++$i) {
    $strategy = new Strategy(function() {
        var_dump($this->value);
    });

    $strategy->run();
}

这里是一个使用静态计数器的更复杂的例子:

演示:https://3v4l.org/smcDi

interface StrategyInterface
{
    public function run();
}

class Strategy implements StrategyInterface
{
    protected ?string $value = null;
    private static $counter = 0;

    public function __construct(private Closure $closure)
    {
        echo "Strategy Counter: ", ++self::$counter, PHP_EOL;
        $this->value = (string)rand(1, 100);
    }

    public function run()
    {
        $this->closure->call($this);
    }

    public function __destruct()
    {
        echo "Strategy Counter: ", --self::$counter, PHP_EOL;
    }
}

$strategy1 = new Strategy(function () {
    var_dump($this->value);
});

$strategy2 = new Strategy(function () {
    var_dump($this->value);
});

$strategy3 = new Strategy(function () {
    var_dump($this->value);
});


$strategy1->run(); // counter still 3, because 3 are created
$strategy1 = null; // destroy the first strategy, counter is 2
$strategy2->run();
unset($strategy2); // destroy the second strategy, counter is 1
$strategy3->run();

$strategy4 = new Strategy(function () { // create a new strategy, counter is 2
    var_dump($this->value);
});

// program ends, counter goes down to 0