使用变量[duplicate]动态访问静态属性

Question

This question already has an answer here:

• Accessing a class constant using a simple variable which contains the name of the constant 5 answers

I'm trying to dynamically access a static namespaced property (using delight-im's auth). Possible values could be:

\Delight\Auth\Role::ADMIN
\Delight\Auth\Role::USER

etc

I want to name the ADMIN part dynamically, as such:

\Delight\Auth\Role::$role

But PHP is telling me:

 Access to undeclared static property: Delight\Auth\Role::$role

So I tried to use a variable variable as such:

 \Delight\Auth\Role::$$val

(two $s) and the error changes to:

 Access to undeclared static property: Delight\Auth\Role::$ADMIN

So as you can see the variable is resolved, but there is a $ inserted in there still. I'm using PHP 5.6.37 if that makes a difference.

Is there a way to access static properties dynamically like this?

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Answer 1

You're mixing up your terminology. The syntax you're using is accessing a class's static property, but you're describing features of a class constant.

Static properties are mutatable variables stored on the class. Example from the PHP manual:

<?php
class Foo
{
    public static $my_static = 'foo';

    public function staticValue() {
        return self::$my_static;
    }
}

You'd reference $my_static like this: Foo::$my_static, which is what you're doing.

Class constants seems to be what you're describing. Example from the PHP manual:

<?php
class MyClass
{
    const CONSTANT = 'constant value';

    function showConstant() {
        echo  self::CONSTANT . "
";
    }
}

You'd reference CONSTANT like this: MyClass::CONSTANT.

Here's a better answer describing how to reference class constants dynamically, which is what you're attempting to do.