isset()和__isset()有什么区别? [英] What is the difference between isset() and __isset()?

问题描述

我需要了解魔术函数__isset()和普通函数isset().其实php语言构造isset()和php魔术方法__isset()之间的真正区别是什么?当我在Google上搜索时，他们告诉我们__isset()是一个魔术函数.普通的php函数和php中的魔术函数有什么区别?

I need to know about magic function __isset() and normal function isset(). Actually what is the real difference between php language construct isset() and php magic method __isset() ? When I google it they told that __isset() is a magic function. What are difference between common php functions and magic functions in php?

推荐答案

isset()

这是一种用于检查变量或类属性的初始化的语言构造:

isset()

It is a language construct that checks the initialization of variables or class properties:

$a = 10;

isset($a);     // true
isset($a, $b); // false

class Test
{
    public $prop = 10;
}

$obj = new Test;
isset($obj->prop); // true

---

__isset()

这是一种魔术方法，当isset()或empty()检查不存在或无法访问的类属性时会调用该方法:

---

__isset()

It is a magic method that is invoked when isset() or empty() check non-existent or inaccessible class property:

class Test
{
    public function __isset($name) {
        echo "Non-existent property '$name'";
    }
}

$obj = new Test;
isset($obj->prop); // prints "Non-existent property 'prop'" and return false

---

差异:

           isset()                               __isset()

Language construct                    | Magic method
                                      |
Always return bool                    | Result depends on custom logic*
                                      |
Must be invoked in code               | Called automatically by event
                                      |
Unlimited number of parameters        | Has only one parameter
                                      |
Can be used in any scope              | Must be defined as method**
                                      |
Is a reserved keyword                 | Not a reserved keyword
                                      |
Can't be redefined (Parse error)      | Can be redefined in extended class***

__isset()结果将被自动转换为为bool.

实际上，您可以定义自定义函数__isset()，但它与magic方法无关.

Actually you can define custom function __isset() but it has nothing to do with the magic method.

请参见此示例.

与普通功能不同，只能在类范围内定义并在特定事件上自动调用，例如:不可访问的方法调用，类序列化，在不可访问的属性上使用unset()时等.另请参见此官方文档:超载.

Unlike common functions can be defined only in class scope and invoked automatically on specific events such as: inaccessible method invocation, class serialization, when unset() used on inaccessible properties and so on. See also this official documentation: Overloading.

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