PHP 魔术方法示例

Question

我从 Zend PHP 学习指南中得到了这个问题，但找不到合适的解释...

<?php
    class Magic {
        public $a = "A";
        protected $b = array("a"=>"A", "b"=>"B", "c"=>"C");
        protected $c = array(1,2,3);

        public function __get($v) {
            echo "$v,";
            return $this->b[$v];
        }
        public function __set($var, $val) {
            echo "$var: $val,";
            $this->$var = $val;
        }
    }

    $m = new Magic();
    echo $m->a.",".$m->b.",".$m->c.",";
    $m->c = "CC";
    echo $m->a.",".$m->b.",".$m->c;
?>

根据指南，解决方案应为“b,c,A,B,C,c: CC,b,c,A,B,C”。我不明白为什么 - 也许你知道？我的意图是 $m->a 的第一次调用会导致结果“a”，但这显然是错误的...

Answer 1

由于 __get() 调用了 echo，一些数据在类外的 echo 被调用之前被输出。

通过 echo 单步执行第一行，它是这样执行的:

$m->a   "A" is concatenated
","     "," is concatenated
$m->b   "b," is echoed, "B" is concatenated
","     "," is concatenated
$m->c   "c," is echoed, "C" is concatenated
"m"     "," is concatenated

此时，b,c,已经被回显，并且值为A,B,Cm的字符串现在显示。