Question

我在Zend PHP学习指南中有这个问题，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”。我无法弄清楚为什么 - 也许你呢？我的意图是$ m-＆gt; 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，因此在调用类外的echo之前会输出一些数据。

单步执行echo的第一行，这就是它的执行方式：

$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,已被echo编辑，现在显示值为A,B,Cm的字符串。

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