PHP变量引用之谜

Question

运行以下代码:

<?php
$a = array('yes');
$a[] = $a;
var_dump($a);

输出:

array(2) {
  [0]=>
  string(3) "yes"
  [1]=>
  array(1) {
    [0]=>
    string(3) "yes"
  }
}

运行以下代码:

<?php
$a = array('no');
$b = &$a;
$a[] = $b;
$a = array('yes');
$a[] = $a;
var_dump($a);

输出:

array(2) {
  [0]=>
  string(3) "yes"
  [1]=>
  array(2) {
    [0]=>
    string(3) "yes"
    [1]=>
    *RECURSION*
  }
}

我已经为 $a 重新分配了值，为什么会有 RECURSION 循环引用？

Answer 1

要删除引用，您需要调用 unset。在 $a = array('yes'); 之后没有 unset $a 仍然与 $b 绑定(bind)并且它们仍然是引用。所以第二部分的行为与第一部分相同。

Note, however, that references inside arrays are potentially dangerous. Doing a normal (not by reference) assignment with a reference on the right side does not turn the left side into a reference, but references inside arrays are preserved in these normal assignments.

http://php.net/manual/en/language.references.whatdo.php