PHP 函数的函数指针用于解决哪些具体问题？

<?php // 回调函数function greet($name) {  echo "Hello, $name!";}// 调用回调函数call_user_func('greet', 'John'); // 输出：Hello, John!?>

<?php class MyClass {  // 添加事件监听器  public function addEventListener($event, $listener) {    $this->listeners[$event][] = $listener;  }  // 触发事件  public function triggerEvent($event, $args) {    foreach ($this-&gt;listeners[$event] ?? [] as $listener) {      call_user_func($listener, $args);    }  }}$obj = new MyClass();$obj-&gt;addEventListener('click', function() { echo 'Click event triggered!'; });$obj-&gt;triggerEvent('click'); // 输出：Click event triggered!

<?php // 比较函数function compareAge($person1, $person2) {  return $person1['age'] - $person2['age'];}// 对数组按年龄排序$people = [  ['name' => 'John', 'age' =&gt; 30],  ['name' =&gt; 'Mary', 'age' =&gt; 25],  ['name' =&gt; 'Bob', 'age' =&gt; 35],];usort($people, 'compareAge');// 输出排序后的数组foreach ($people as $person) {  echo $person['name'] . ': ' . $person['age'] . "";}?&gt;