PHP 回调、匿名函数和闭包

<?php
class Product{
    public $name;
    public $price;
    
    function __construct($name, $price){
        $this->name = $name;
        $this->price = $price;
    }
}

class ProcessSale{
    private $callbacks;
    
    function registerCallback($callback){
        if(!is_callable($callback)){
            throw new Exception("callback not callable");
        }
        $this->callbacks[] = $callback;
    }
    
    function sale($product){
        print "{$product->name}:processing 
";
        foreach ($this->callbacks as $callback){
            call_user_func($callback, $product);
        }
    }
}

$logger = create_function('$product', 'print "   logging ({$product->name})
";');

$processor = new ProcessSale();
$processor->registerCallback($logger);

$processor->sale(new Product("shoes", 6));
print "
";
$processor->sale(new Product("coffee", 6));


$logger2 = function($product){
    print "  logging ({$product->name})
";
};

$processor = new ProcessSale();

$processor = new ProcessSale();
$processor->registerCallback($logger2);

$processor->sale(new Product("shoes", 6));
print "
";
$processor->sale(new Product("coffee", 6));

class Mailer{
    function doMail($product){
        print "  mailing ({$product->name})
";
    }
}

$processor = new ProcessSale();
$processor->registerCallback(array(new Mailer(), "doMail"));

$processor->sale(new Product("shoes", 6));
print "
";
$processor->sale(new Product("coffee", 6));

class Totalizer{
    static function warnAmount(){
        return function($product){
            if ($product->price > 5){
                print "  reached high price: {$product->price}
";
            }
        };
    }
}

$processor = new ProcessSale();
$processor->registerCallback(Totalizer::warnAmount());

//.....

class TotalizerNew{
    static function warnAmount($amt){
        $count = 0;
        return function($product) use ($amt, &$count){
            $count += $product->price;
            print "  count: $count
";
            if ($count > $amt){
                print "  high price reached:{$count}
";
            }
        };
    }
}

$processor = new ProcessSale();
$processor->registerCallback(TotalizerNew::warnAmount(8));

$processor->sale(new Product("shoes", 6));
print "
";
$processor->sale(new Product("coffee", 6));