<?php //定义callback函数，分数大的元素排名靠前 function cmp_score($a, $b) {     if ($a['score'] == $b['score']) {         return 0;     }     //-1表示排在前面     return ($a['score'] > $b['score']) ? -1 : 1; } $list = [     ['name' => 'Tom', 'score' => 80],     ['name' => 'Bob', 'score' => 60],     ['name' => 'David', 'score' => 90],     ['name' => 'LiLy', 'score' => 55], ]; //'cmp_score'作为一个callback类型的参数 usort($list, 'cmp_score'); foreach ($list as $index => $item) {     echo "Name: {$item['name']}\tScore: {$item['score']}\tRank: " . ($index + 1) . PHP_EOL; }