如何在PHP的类属性中使用类常量? [英] How to use a class constant into a class attribute in PHP?

问题描述

这是不起作用的代码:

class MyClass
{
    const myconst = 'somevalue';

    private $myvar = array( 0 => 'do something with '.self::myconst );
}

似乎类常量在编译时"不可用，而仅在运行时可用. 有人知道有什么解决方法吗? (定义将无效)

Seems that class constants are not available at "compile time", but only at runtime. Does anyone know any workaround ? (define won't work)

谢谢

推荐答案

类声明中的问题不是使用常量，而是使用表达式.

The problem in your class declaration is not that you are using a constant, but that you are using an expression.

类成员变量称为属性". (...)通过使用关键字public，protected或private之一定义，后跟普通变量声明.该声明可以包含一个初始化，但是该初始化必须是一个常量值-也就是说，它必须能够在编译时进行评估，并且必须不依赖于运行时信息才能被评估.

Class member variables are called "properties". (...) They are defined by using one of the keywords public, protected, or private, followed by a normal variable declaration. This declaration may include an initialization, but this initialization must be a constant value--that is, it must be able to be evaluated at compile time and must not depend on run-time information in order to be evaluated.

例如，此简单声明将不会编译(解析错误):

This simple declaration, for example, will not compile (parse error):

class MyClass{
    private $myvar = 3+2;
}

但是，如果我们更改类声明以使用简单常量，而不是使用与该常量串联的字符串，它将按预期工作.

But if we alter your class declaration to use the simple constant, rather than a string concatenated with that constant it will work as expected.

class MyClass{
    const myconst = 'somevalue';
    public $myvar = array( 0 => self::myconst );
}

$obj = new MyClass();
echo $obj->myvar[0];

作为解决方法，您可以在构造函数中初始化属性:

As a work-around you could initialize your properties in the constructor:

class MyClass{
    const myconst = 'somevalue';
    public $myvar;

    public function __construct(){
        $this->myvar = array( 0 => 'do something with '.self::myconst );
    }
}
$obj = new MyClass();
echo $obj->myvar[0];

希望这对您有帮助，
阿林

I hope this helps you,
Alin

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