php - 如何在 PHP 中将类常量用于类属性？

Question

这是行不通的代码:

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。有谁知道任何解决方法？ (定义不起作用)

谢谢

Answer 1

类声明中的问题不是您使用的是常量，而是您使用的是表达式。

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，这个简单的声明将不会编译(解析错误):

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

但是，如果我们更改您的类声明以使用简单常量，而不是与该常量连接的字符串，它将按预期工作。

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

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

作为变通方法，您可以在构造函数中初始化您的属性:

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];

希望对你有帮助，
阿林