在PHP中对象真的是按引用传递的吗

PHPclass A {};class B {};$a = new A;$b = $a;    $b->testA = "Changed Class A";/* * 此时$a,$b的关系： *        +-----------+      +-----------------+ * $a --> | object id | ---> | object(Class A) | *        +-----------+      +-----------------+ *                               ^ *        +-----------+          | * $b --> | object id | ---------+ *        +-----------+     * * */$c = new B;$a = $c;$a->testB = "Changed Class B";/* * 此时$a,$b,$c的关系： *        +-----------+      +-----------------+ * $b --> | object id | ---> | object(Class A) | *        +-----------+      +-----------------+ *                                *        +------------+           * $a --> | object id2 | -------------+ *        +------------+              | *                                    v *        +------------+      +-----------------+ * $c --> | object id2 | ---> | object(Class B) | *        +------------+      +-----------------+ */echo "object a: "; var_dump($a); //["testB"]=> string(15) "Changed Class B"echo "object b: "; var_dump($b); //["testA"] => string(15) "Changed Class A"echo "object c: "; var_dump($c); //["testB"]=> string(15) "Changed Class B"//如果对象是按照引用传递的，那么$a, $b, $c输出的内容应该一样，事实上结果并非如此。 看下面通过引用传递对象的列子：<?php$aa = new A;$bb = &$aa;  // 引用 $bb->testA = 2;/* * 此时$aa, $bb的关系： * *         +-----------+      +-----------------+ * $bb --> | object id | ---> | object(Class A) | *         +-----------+      +-----------------+ *              ^                   *              | * $aa ---------+  * * */$cc = new B;$aa = $cc;$aa->testB = "Changed Class B";/* * 此时$aa, $bb, $cc的关系： * *         +-----------+      +-----------------+ *         | object id | ---> | object(Class A) | *         +-----------+      +-----------------+ *               * $bb ---->-----+       *               | * $aa ---->-----+ *               |   *               v    *         +------------+       *         | object id2 | --------------+  *         +------------+               | *                                      v *         +------------+      +-----------------+ * $cc --> | object id2 | ---> | object(Class B) | *         +------------+      +-----------------+ */echo "object aa: "; var_dump($aa); //["testB"]=>string(15) "Changed Class B"echo "object bb: "; var_dump($bb); //["testB"]=>string(15) "Changed Class B"echo "object cc: "; var_dump($cc); //["testB"]=>string(15) "Changed Class B"//此时$aa，$bb，$cc三者内容完全一样，所以可以看出对象默认并不是按照引用传递，要尽快走出这个误区。