PHP 一种访问私有属性的方法

  在鸟哥《深入理解PHP原理之对象(一)》看到一段挺有意思的代码

<?php
class Foo {
    private $_name = "laruence";
    protected $_age = 28;
}
$foo = new Foo();
$arr = (array) $foo;
var_dump($arr["\0Foo\0_name"]);
var_dump($arr["\0*\0_age"]);
//output:
string(8) "laruence"
int(28)

  至于这算不算BUG本文就不议论了，有兴趣的可以看看这里 (见:  Bug #44273 access to private and protected class variables allowed when casting to array ):  下面有相关议论

  那为什么对象转成数组以后能通过构建特殊的key去访问呢？直接看关键代码吧! (已下代码PHP版本为:  5.4.27)

/* Zend/zend_API.c +3361*/
ZEND_API int zend_declare_property_ex(zend_class_entry *ce, const char *name, int name_length, zval *property, int access_type, const char *doc_comment, int doc_comment_len TSRMLS_DC) /* {{{ */
{
.....
	switch (access_type & ZEND_ACC_PPP_MASK) {
		case ZEND_ACC_PRIVATE: {
				char *priv_name;
				int priv_name_length;

				zend_mangle_property_name(&priv_name, &priv_name_length, ce->name, ce->name_length, name, name_length, ce->type & ZEND_INTERNAL_CLASS);
				property_info.name = priv_name;
				property_info.name_length = priv_name_length;
			}
			break;
		case ZEND_ACC_PROTECTED: {
				char *prot_name;
				int prot_name_length;

				zend_mangle_property_name(&prot_name, &prot_name_length, "*", 1, name, name_length, ce->type & ZEND_INTERNAL_CLASS);
				property_info.name = prot_name;
				property_info.name_length = prot_name_length;
			}
			break;
		case ZEND_ACC_PUBLIC:
			if (IS_INTERNED(name)) {
				property_info.name = (char*)name;
			} else {
				property_info.name = ce->type & ZEND_INTERNAL_CLASS ? zend_strndup(name, name_length) : estrndup(name, name_length);
			}
			property_info.name_length = name_length;
			break;
	}
.....
	zend_hash_quick_update(&ce->properties_info, name, name_length+1, h, &property_info, sizeof(zend_property_info), NULL);

	return SUCCESS;
}

  可以看到当属性是private和protected时候调用zend_mangle_property_name来构造property_info.name (转换后的key)，而它们第3，4个参数也不一样，private传入的是类名，而protected传入的是'*'字符。在看看zend_mangle_property_name函数的实现就一目了然了。

/* Zend/zend_compile.c +5037 */
ZEND_API void zend_mangle_property_name(char **dest, int *dest_length, const char *src1, int src1_length, const char *src2, int src2_length, int internal) /* {{{ */
{
	char *prop_name;
	int prop_name_length;

	prop_name_length = 1 + src1_length + 1 + src2_length;
	prop_name = pemalloc(prop_name_length + 1, internal);
	prop_name[0] = '\0';
	memcpy(prop_name + 1, src1, src1_length+1);
	memcpy(prop_name + 1 + src1_length + 1, src2, src2_length+1);

	*dest = prop_name;
	*dest_length = prop_name_length;
}
/* }}} */

  所以对象的private属性我们可以强制转换为array后通过 $obj["\0类名\0属性名"] 来访问，而protected则是 $obj["\0*\0属性名"] 

  至于流程可以通过"zend_do_declare_property"关键字到 http://lxr.php.net/ 搜索, 大概就是  zend_do_declare_property->zend_declare_property_ex->zend_mangle_property_name

  嗯，好像也没写什么的样子，一些细节比如property_info被zend_hash_quick_update, 类型的转换都没理解清楚。