.. _(expression)::class-cannot-be-used-in-constant-expressions:

(expression)::class cannot be used in constant expressions
----------------------------------------------------------
 
.. meta::
	:description:
		(expression)::class cannot be used in constant expressions: This error appears when the value of a constant is not entirely static, but may depend on context.
	:og:image: https://php-errors.readthedocs.io/en/latest/_static/logo.png
	:og:type: article
	:og:title: (expression)::class cannot be used in constant expressions
	:og:description: This error appears when the value of a constant is not entirely static, but may depend on context
	:og:url: https://php-errors.readthedocs.io/en/latest/messages/%28expression%29%3A%3Aclass-cannot-be-used-in-constant-expressions.html
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	:twitter:title: (expression)::class cannot be used in constant expressions
	:twitter:description: (expression)::class cannot be used in constant expressions: This error appears when the value of a constant is not entirely static, but may depend on context
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Description
___________
 
This error appears when the value of a constant is not entirely static, but may depend on context. In this case, the ``self::A`` will only be known when the trait t is used in a class.

Example
_______

.. code-block:: php

   <?php
   
   trait T {
       const A = parent::class;
       const B = self::A::class;
   }
   
   ?>

Solutions
_________

+ Keep values of constants simple.

Changed Behavior
________________

This error may appear following an evolution in behavior, in previous versions. See ` <https://php-changed-behaviors.readthedocs.io/en/latest/behavior/.html>`_.