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php 类型运算符instanceof

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Release： 2016-06-13 10:54:32
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类型运算符instanceof在某些php书籍中貌似没有提到啊，在细说php中也只是提到没有细讲，摘抄下手册中的，以作备注。

instanceof 运算符是 PHP 5 引进的。在此之前用 is_a()，但是 is_a() 已经过时了，最好用 instanceof。

 

1、用来确定一个变量是否属于某个类的实例；

2、用来确定一个变量是否是继承自某一父类的子类的实例；

3、用来确定一个变量是否是实现了某个接口的对象的实例。

 

在 PHP 5.1.0之前，如果要检查的类名称不存在，instanceof 会调用 __autoload()。另外，如果该类没有被装载则会产生一个致命错误。可以通过使用动态类引用(dynamic class reference)或用一个包含类名的字符串变量来避开这种问题： 

 

Example #6 避免 PHP 5.0 中 instanceof 引起的类名查找和致命错误问题

 

$d = 'NotMyClass';

var_dump($a instanceof $d); // no fatal error here

?> 

Related labels：
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