PHP中的self :: $ bar和static :: $ bar有什么区别?

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问题描述

在下面的示例中，使用self和static有什么区别?

What is the difference between using self and static in the example below?

class Foo
{
    protected static $bar = 1234;

    public static function instance()
    {
        echo self::$bar;
        echo "\n";
        echo static::$bar;
    }

}

Foo::instance();

产生

1234
1234

推荐答案

使用self引用类成员时，即表示您在其中使用关键字的类.在这种情况下，您的Foo类定义了一个受保护的静态属性，称为$bar.当您在Foo类中使用self来引用该属性时，您所引用的是同一类.

When you use self to refer to a class member, you're referring to the class within which you use the keyword. In this case, your Foo class defines a protected static property called $bar. When you use self in the Foo class to refer to the property, you're referencing the same class.

因此，如果您尝试在Foo类中的其他位置使用self::$bar，但是您有一个Bar类，其属性值不同，则它将使用Foo::$bar而不是Bar::$bar，这可能不会就是你想要的:

Therefore if you tried to use self::$bar elsewhere in your Foo class but you had a Bar class with a different value for the property, it would use Foo::$bar instead of Bar::$bar, which may not be what you intend:

class Foo
{
    protected static $bar = 1234;
}

class Bar extends Foo
{
    protected static $bar = 4321;
}

当您通过static 调用方法时，您正在调用名为后期静态绑定(在PHP 5.3中引入).

When you call a method via static, you're invoking a feature called late static bindings (introduced in PHP 5.3).

在上述情况下，使用self将导致Foo::$bar(1234).使用static会导致Bar::$bar(4321)，因为使用static时，解释器会在运行时考虑Bar类中的重新声明.

In the above scenario, using self will result in Foo::$bar(1234).And using static will result in Bar::$bar (4321) because with static, the interpreter takes takes into account the redeclaration within the Bar class during runtime.

您通常将后期静态绑定用于方法甚至类本身，而不是属性，因为您通常不会在子类中重新声明属性；可以在以下相关问题中找到使用static关键字调用后期绑定的构造函数的示例:

You typically use late static bindings for methods or even the class itself, rather than properties, as you don't often redeclare properties in subclasses; an example of using the static keyword for invoking a late-bound constructor can be found in this related question: New self vs. new static

但是，这并不排除将static与属性一起使用.

However, that doesn't preclude using static with properties as well.

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