在php中使用callable(use of callable in php)

 我试图在下面的实现中模仿php的内置usort函数定义： 
 
class heapSort {
    static function hsort(array &$array, callable $cmp_function){
       // logic
    }
}

class utility{
    static function mycomparator(){
        // logic
    }
}

$array = array(5,3,8,1);
$callback = array('utility','mycomparator');
heapSort::hsort($array, $callback);
 
 虽然变量$callback是“可调用的”，但为什么我会遇到致命错误？ 
 
 
 
 传递给heapSort :: hsort（）的参数2必须是可调用的实例。 
 
 
 更具体地说，如何使$variable可以调用/类型化？ 

I am trying to mimic php's inbuilt usort function definition in my implementation below:
 
class heapSort {
    static function hsort(array &$array, callable $cmp_function){
       // logic
    }
}

class utility{
    static function mycomparator(){
        // logic
    }
}

$array = array(5,3,8,1);
$callback = array('utility','mycomparator');
heapSort::hsort($array, $callback);
 
While the variable $callback is "callable" why do I get below fatal error?
 
 
 
Argument 2 passed to heapSort::hsort() must be an instance of callable.
 
 
More specifically, how do I make/typecast a $variable to callable?

原文：https://stackoverflow.com/questions/15818301