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0-instanceof is used to determine whether a PHP variable is an instantiated object of a certain class

1-instanceof can also be used to determine whether a variable is an instantiated object of a class that inherits from a parent class

2-Lastly, instanceof can also be used to determine whether a variable is an instantiated object of a class that implements an interface

http://php.net/manual/en/language.operators.type.php

http://php.net/manual/zh/language.operators.type.php

类型运算符

instanceof 用于确定一个 PHP 变量是否属于某一类 class 的实例

instanceof　也可用来确定一个变量是不是继承自某一父类的子类的实例

最后，instanceof也可用于确定一个变量是不是实现了某个接口的对象的实例

<?php

interface MyInterface
{
}

class MyClass implements MyInterface
{
}

$a = new MyClass;

var_dump($a instanceof MyClass);
var_dump($a instanceof MyInterface);

bool(true) bool(true)

<?php

interface MyInterface
{
}

class MyClass implements MyInterface
{
}

$a = new MyClass;
$b = new MyClass;
$c = 'MyClass';
$d = 'NotMyClass';

var_dump($a instanceof $b); // $b is an object of class MyClass
var_dump($a instanceof $c); // $c is a string 'MyClass'
var_dump($a instanceof $d); // $d is a string 'NotMyClass'

bool(true) bool(true) bool(false)

instanceof does not throw any error if the variable being tested is not an object, it simply returns FALSE. Constants, however, are not allowed.

如果被检测的变量不是对象，instanceof 并不发出任何错误信息而是返回 FALSE。不允许用来检测常量。

<?php
$a = 1;
$b = NULL;
$c = imagecreate(5, 5);
var_dump($a instanceof stdClass); // $a is an integer
var_dump($b instanceof stdClass); // $b is NULL
var_dump($c instanceof stdClass); // $c is a resource
var_dump(FALSE instanceof stdClass);