如何在 PHP 5.2 中的子类中创建一个常量，以便在父类中找到的方法中使用？

发布于 2024-10-07 06:11:02 字数 890 浏览 4 评论 0原文

编辑：
*注意：不幸的是，我暂时使用 PHP 5.2。我找不到提供 5.3 的像样便宜主机...

在 PHP 中，self 指的是定义被调用方法的类。这意味着，如果您不重写子类中的方法，则关键字 self 将引用父类，即使从子类调用也是如此。

例如，此代码：

<?php

class ParentClass {
  const NAME = "ParentClass";
  public function showName() {
    echo self::NAME . "<br />\n";
  }
}

class ChildClass extends ParentClass {
  const NAME = "ChildClass";
  public function __construct() {
    echo self::NAME . "<br />\n";
  }
}

$test = new ChildClass();
$test->showName();

?>

将创建此输出：

ChildClass
ParentClass

我想要做的是创建一个默认方法（例如上例中的 showName() ），该方法存在于父类中，并具有定义默认值的常量使用。在子级中，我希望能够重写这些常量（请注意上面子级定义中的 const），并在我在子级实例上调用方法时使用这些值。

简而言之，我怎样才能使上述示例的输出...

ChildClass
ChildClass

...而不必在子级中复制父级的代码？

原文

Edit:
*Note: I'm using PHP 5.2 for the time being, unfortunately. I can't find a decent cheap host offering 5.3...

In PHP, self refers to the class in which the called method is defined. This means that if you don't override a method in the child class, the keyword self will refer to the parent class, even when called from the child.

For example, this code:

<?php

class ParentClass {
  const NAME = "ParentClass";
  public function showName() {
    echo self::NAME . "<br />\n";
  }
}

class ChildClass extends ParentClass {
  const NAME = "ChildClass";
  public function __construct() {
    echo self::NAME . "<br />\n";
  }
}

$test = new ChildClass();
$test->showName();

?>

Will create this output:

ChildClass
ParentClass

What I want to do is to create a default method (e.g. showName() in the example above) which exists in a parent class with constants defining default values to use. In the child, I want to be able to override these constants (note the const in the child definition above), and have those values be used when I call the method on an instance of the child.

In short, how can I make it so that the output of the above sample would be...

ChildClass
ChildClass

...without having to duplicate the code of the parent within the child?

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本宫微胖 2024-10-14 06:11:02

尝试

function showName() {
   return static::NAME;
}

使用后期静态绑定：

从 PHP 5.3.0 开始，PHP 实现了
称为后期静态绑定的功能
可以用来参考
在静态上下文中调用类
继承。
更准确地说，后期静态绑定
通过存储命名的类来工作
最后一个“非转接呼叫”。如果出现以下情况
静态方法调用，这是类
明确命名（通常是
:: 运算符的左侧）；以防万一
非静态方法调用中，它是
对象的类。一个“转发
call” 是静态的，即
自我介绍::, 家长::,
static::，或者，如果在班级中上升
层次结构，forward_static_call()。这
函数 get_used_class() 可以是
用于检索字符串
被调用类的名称和 static::
介绍其范围。

编辑：对于 5.2.x

如果您没有 5.3.0，您将无法利用此功能。一种常见的~~hack~~解决方案是创建一个由子类名引用的静态缓存（例如private static $statics = array()）。它要求您跟踪对象继承以覆盖 __construct 上的值，并显式定义哪些静态是“可继承的”。例如，SilverStripe 在 Sapphire ORM 中使用此技术来绕过 PHP 静态绑定限制。他们定义了一个基本对象类，以及各种静态变量管理功能。

Try

function showName() {
   return static::NAME;
}

This uses late static binding:

As of PHP 5.3.0, PHP implements a
feature called late static bindings
which can be used to reference the
called class in a context of static
inheritance.
More precisely, late static bindings
work by storing the class named in the
last "non-forwarding call". In case of
static method calls, this is the class
explicitly named (usually the one on
the left of the :: operator); in case
of non static method calls, it is the
class of the object. A "forwarding
call" is a static one that is
introduced by self::, parent::,
static::, or, if going up in the class
hierarchy, forward_static_call(). The
function get_called_class() can be
used to retrieve a string with the
name of the called class and static::
introduces its scope.

EDIT: For 5.2.x

If you don't have 5.3.0 you won't be able to take advantage of this. One common ~~hack~~ solution is to create a static cache (e.g. private static $statics = array()) referenced by child class name. It requires you to track object inheritance to override the value on __construct, and to explicitly define which statics are 'inheritable'. For example, SilverStripe uses this technique in the Sapphire ORM to get around PHP static binding limitations. They define a base Object class, and various static var management functions.

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爱你不解释 2024-10-14 06:11:02

我相信您的情况的相应语法盐是：

print constant(get_class($this)."::NAME");

I believe the according syntactic salt for your case is:

print constant(get_class($this)."::NAME");

回复收藏 0 原文

浅暮の光 2024-10-14 06:11:02

也许这只是因为你的例子很短，但“自我”引用似乎并不需要。

我只想这样做：

class ParentClass {
  public function showName() {
    echo $this->name() . "<br />\n";
  }

  public static function name() {
    return "ParentClass";
  }
}

class ChildClass extends ParentClass {
  public function __construct() {
    echo $this->name() . "<br />\n";
  }
  public static function name() {
    return "ChildClass";
  }
}

$test = new ChildClass();
$test->showName();

输出：

ChildClass
ChildClass

Maybe it's just because of your short example but the "self" referencing doesn't seem needed.

I would just do this:

class ParentClass {
  public function showName() {
    echo $this->name() . "<br />\n";
  }

  public static function name() {
    return "ParentClass";
  }
}

class ChildClass extends ParentClass {
  public function __construct() {
    echo $this->name() . "<br />\n";
  }
  public static function name() {
    return "ChildClass";
  }
}

$test = new ChildClass();
$test->showName();

Output: