SplHeap::compare

This method is abstract, and in PHP 8.0+ its parameters are of type `mixed`, you can not change their types to types other than `mixed` when `extends`ing SplHeap.

The following example emits an error saying "Fatal error: Declaration of WuXianchengHeap::compare(string $one, string $two): int must be compatible with SplHeap::compare(mixed $value1, mixed $value2)".

<?php
    class WuXianchengHeap extends SplHeap{
        public function __construct(Iterator $iterator){
            foreach($iterator as $item){
                $this->insert($item);
            }
        }
        public function compare(string $one, string $two):int{
            return -1 * strNatCaseCmp($one, $two);
        }
    }
?>