php函数引用传值

<?php
function &fun(){
    static $a=10;
    return $a;
}
$f=&fun();
var_dump($f); //10
$f=100;
var_dump(fun());  //100

?>

<?php
function fun(){
    static $a=10;
    return $a;
}
$f=&fun(); //Strict standards: Only variables should be assigned by reference
var_dump($f);//10
?>

<?php
function &fun(){
    static $a=10;
    return $a;
}
$f=fun();
var_dump($f);//10
$f=100;
var_dump(fun());//10
?>