PHP 魔术方法示例

Question

PHP 魔术方法示例

11

我从Zend PHP学习指南上看到这个问题，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;
?>

根据指导，解决方案应该是"b,c,A,B,C,c：CC,b,c,A,B,C"。我想不出原因——也许你能想出来？我的意图是第一次调用$m->a会导致结果为"a"，但这显然是错误的...

- Jan Petzold

您提供的代码将输出 "b,c,A,B,Cmc: CC,b,c,A,B,C"（参见此证明）。这是打印指南中的一个错字还是确切的内容？ - Tadeck

你是对的 - 是个小笔误。现在已经正确了 http://codepad.org/H91fpj8q - Jan Petzold

1个回答

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- user142162 · Accepted Answer

由于__get()调用echo，因此在类外部调用echo之前已经输出了一些数据。

通过使用echo逐步执行第一行代码：

$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

在这一点上，b, c已经被echo了，并且显示了值为A,B,Cm的字符串。