设置新值时获取变量的旧值

Question

$variable = "hello";
$variable = changevalue("world");

function changevalue($newvalue) {
     if($variable == "hello") $variable = $newvalue;
}

我知道这是可行的＆amp ;.但是，如果没有在changevalue中添加param＆amp; $变量，有没有办法获得变量的旧值？

Answer 1

$oldvalue = "";
$variable = "hello";

function changevalue($newvalue) {
    global $variable, $oldvalue;

    $oldvalue = $variable; 

    return $newvalue;
}

$variable = changevalue("world");