Call a function only once.

Return a function, which only calls the provided function, $function, if $called is false and sets $called to true.

代码实现

function once($function)
{
  return function (...$args) use ($function) {
    static $called = false;
    if ($called) {
      return;
    }
    $called = true;
    return $function(...$args);
  };
}

使用样例

$add = function ($a, $b) {
  return $a + $b;
};

$once = once($add);

var_dump($once(10, 5)); // 15
var_dump($once(20, 10)); // null