从 PHP5 中的抽象方法访问类常量

发布于 2024-08-22 05:14:12 字数 314 浏览 4 评论 0原文

我试图获取扩展类的常量值，但在抽象类的方法中。像这样：

    abstract class Foo {
        public function method() {
            echo self::constant;
        }
    }

    class Bar extends Foo {
        const constant = "I am a constant";
    }

    $bar = new Bar();
    $bar->method();

但这会导致致命错误。有什么办法可以做到这一点吗？

原文

I'm trying to get the value of a constant of an extending class, but in a method of the abstract class. Like this:

    abstract class Foo {
        public function method() {
            echo self::constant;
        }
    }

    class Bar extends Foo {
        const constant = "I am a constant";
    }

    $bar = new Bar();
    $bar->method();

This however results in a fatal error. Is there any way to do this?

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-小熊_ 2024-08-29 05:14:12

这可以使用 PHP 5.3 中引入的 Late Static Binding 关键字实现。

本质上，self 指的是编写代码的当前类，但 static 指的是代码所在的类正在运行。

我们可以将您的代码片段重写为：

abstract class Foo {
    public function method() {
        echo static::constant;    // Note the static keyword here
    }
}

class Bar extends Foo {
    const constant = "I am a constant";
}

$bar = new Bar();
$bar->method();

但是，这种编码模式很脏，您可能应该在父类和子类之间引入受保护的 api 来来回传输此类信息。

所以从代码组织的角度来看，我更倾向于Morfildur提出的解决方案。

This is possible using the Late Static Binding keyword introduced in PHP 5.3

Essentially, self refers to the current class that the code is written in, but static refers to the class the code is running from.

We could rewrite your code snippet as:

abstract class Foo {
    public function method() {
        echo static::constant;    // Note the static keyword here
    }
}

class Bar extends Foo {
    const constant = "I am a constant";
}

$bar = new Bar();
$bar->method();

However, this pattern of coding is dirty and you should probably instead introduce a protected api between your parent class and subclasses to funnel that kind of information back and forth.

So from a code organization perspective, I would lean more towards the solution that Morfildur put forward.

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寂寞清仓 2024-08-29 05:14:12

这是不可能的。一种可能的解决方案是创建一个虚拟方法，该方法返回子类中所需的值，即

abstract class Foo {
  protected abstract function getBar();

  public function method() {
    return $this->getBar();
  }
}

class Bar extends Foo {
  protected function getBar() {
    return "bar";
  }
}

This is not possible. A possible solution would be to create a virtual method that returns the desired value in the subclasses, i.e.

abstract class Foo {
  protected abstract function getBar();

  public function method() {
    return $this->getBar();
  }
}

class Bar extends Foo {
  protected function getBar() {
    return "bar";
  }
}

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