static:: 和 $this:: 之间的区别 [英] Difference between static:: and $this::

问题描述

我知道 static:: 和 self:: 之间有区别，就像这个例子(来自 https://stackoverflow.com/a/13613718/2342518 )

test();

当使用 static::TEST 时返回 test2，使用 self::TEST 时返回 test1.但是当使用 $this::TEST 时，它也会返回 test2.

static::TEST 可以在静态方法中使用，而 $this::TEST 在使用之前需要一个实例(因此在静态方法).

但是如果不能在静态方法中使用 $this::，static:: 可以在非静态方法中使用(如示例中所示).>

那么，在非静态方法中，static:: 和 $this:: 有什么区别?

<小时>

可选的完整测试

新的 OneStatic(),'二，静态::' =>新的 TwoStatic(),'一，自我::' =>新的自己()，'二，自我::' =>新的 TwoSelf(),'一，$this::' =>新的 OneThis(),'二，$this::' =>新的 TwoThis(),);$results = array();foreach ($objects as $name=>$object)$results[$name] = $object->test();var_dump($results);?>

哪个收益

• 'one, static::' => 'test1'
• '二，静态::' => 'test2'
• 'one, self::' => 'test1'
• '二，自我::' => 'test1'
• 'one, $this::' => 'test1'
• '二，$this::' => 'test2'

so self 指的是定义方法的类，但是在这些非静态方法中 $this:: 和 static:: 没有区别.>

解决方案

不能使用 $this:: 而不是 static 的三种情况::

1.在静态方法中

public 静态函数 test() {返回 $this::MY_CONST;}

输出:

<块引用>

致命错误:未捕获错误:不在对象上下文中使用 $this

2.在非对象上下文中调用的非静态方法

class A {const MY_CONST = 33;公共功能测试(){返回 $this::MY_CONST;}}回声 A::test();//调用这里的测试方法，没有实例化A类

输出:

<块引用>

致命错误:未捕获错误:不在对象上下文中使用 $this

3.当使用特殊的 ::class 关键字

class A {公共功能测试(){返回 $this::class;}}$a = 新 A;echo $a->test();

输出:

<块引用>

致命错误:编译时不允许使用动态类名

注意:在所有三种情况下static:: 都可以使用

---

对于最后一种情况PHP 文档声明:

<块引用>

注意:

使用::class的类名解析是编译时转型.这意味着当时类名字符串是created 尚未发生自动加载.因此，类名即使该类不存在，也会被扩展.没有错误发出那种情况.

所以你不能使用 $this::class 因为你不能引用不存在的类

PHP 8

PHP 8 中的行为已经改变！

出于一致性原因，$this::class 现在提供与 get_class($this) 和 static::class 相同的结果>

https://3v4l.org/iB99O

I know there is a difference between static:: and self:: like in this example ( from https://stackoverflow.com/a/13613718/2342518 )

<?php
class One
{
    const TEST = "test1";
    function test() { echo static::TEST; }
}
class Two extends One
{
    const TEST = "test2";
}

$c = new Two();
$c->test();

Which returns test2 when static::TEST is used and test1 when self::TEST is used. But it also returns test2 when $this::TEST is used.

static::TEST can be used inside a static method, whereas $this::TEST requires an instance before being used (so non-usable in static methods).

But if one cannot use $this:: in static methods, static:: can be used in non-static methods (like in the example).

So, what is the difference between static:: and $this:: in a non static method?

---

Optional complete test

<?php
abstract class AOne
{
    const TEST = "test1";
    abstract public function test();
}
class OneStatic extends AOne
{
    public function test()
    {
        return static::TEST;
    }
}
class TwoStatic extends OneStatic
{
    const TEST = "test2";
}
class OneSelf extends AOne
{
    public function test()
    {
        return self::TEST;
    }
}
class TwoSelf extends OneSelf
{
    const TEST = "test2";
}
class OneThis extends AOne
{
    public function test()
    {
        return $this::TEST;
    }
}
class TwoThis extends OneThis
{
    const TEST = "test2";
}

$objects = array(
    'one, static::'     => new OneStatic(),
    'two, static::'     => new TwoStatic(),
    'one,   self::'     => new OneSelf(),
    'two,   self::'     => new TwoSelf(),
    'one,  $this::'     => new OneThis(),
    'two,  $this::'     => new TwoThis(),
);

$results = array();
foreach ($objects as $name=>$object)
    $results[$name] = $object->test();

var_dump($results);
?>

Which yields

• 'one, static::' => 'test1'
• 'two, static::' => 'test2'
• 'one, self::' => 'test1'
• 'two, self::' => 'test1'
• 'one, $this::' => 'test1'
• 'two, $this::' => 'test2'

So self refers to the class where the method is defined, but there's no difference between $this:: and static:: in these non static methods.

解决方案

There are three cases when you CAN'T use $this:: over static::

1. In static methods

public static function test() {
    return $this::MY_CONST;
}

Output:

Fatal error: Uncaught Error: Using $this when not in object context

2. In none-static methods which get called in none-object context

class A {
    const MY_CONST = 33;
    public function test() {
        return $this::MY_CONST;
    }
}

echo A::test(); // test method here is called without instantiating class A

Output:

Fatal error: Uncaught Error: Using $this when not in object context

3. When using the special ::class keyword

class A {
    public function test() {
        return $this::class;
    }
}

$a = new A;
echo $a->test();

Output:

Fatal error: Dynamic class names are not allowed in compile-time

Note: in all the three cases static:: will work

---

For the last case PHP Documentation states that:

Note:

The class name resolution using ::class is a compile time transformation. That means at the time the class name string is created no autoloading has happened yet. As a consequence, class names are expanded even if the class does not exist. No error is issued in that case.

So you can't use $this::class because you can't reference to non-existent classes

PHP 8

The behavior in PHP 8 has changed!

For consistency reasons $this::class now provides the same result as get_class($this) and static::class

https://3v4l.org/iB99O

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