.. _illegal-method-name:

Illegal method name
-------------------
 
.. meta::
	:description:
		Illegal method name: PHP 8.
	:og:image: https://php-errors.readthedocs.io/en/latest/_static/logo.png
	:og:type: article
	:og:title: Illegal method name
	:og:description: PHP 8
	:og:url: https://php-errors.readthedocs.io/en/latest/messages/illegal-method-name.html
	:og:locale: en
	:twitter:card: summary_large_image
	:twitter:site: @exakat
	:twitter:title: Illegal method name
	:twitter:description: Illegal method name: PHP 8
	:twitter:creator: @exakat
	:twitter:image:src: https://php-errors.readthedocs.io/en/latest/_static/logo.png

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Description
___________
 
PHP 8.5 allows first-class callable syntax (``(...)``) to be used inside a constant expression, so that a static method call can be turned into a ``Closure`` at compile time. To build that closure, the compiler needs the method name as a string that it can resolve at compile time.

Here, the braced expression ``{0}`` is a compile-time constant, but it is an integer, not a string, so it cannot be used as a method name. PHP reports this as an illegal method name.

This differs from 'Cannot use dynamic method name in constant expression', which is reported when the braced expression cannot be resolved to a constant value at all (for example, because it depends on a variable or is a non-scalar value such as an array).

Example
_______

.. code-block:: php

   <?php
   
   class X {
       public static function foo() { return 1; }
   }
   
   const C = X::{0}(...);
   
   var_dump(C);
   
   ?>

Solutions
_________

+ Use a string, instead of a number or another scalar, for the method name.
+ Ensure the method name is a literal string, or an expression that PHP can resolve to one at compile time.

Related Error Messages
______________________

+ :ref:`cannot-use-dynamic-method-name-in-constant-expression`
+ :ref:`illegal-function-name`
+ :ref:`cannot-use-dynamic-function-name-in-constant-expression`

Changed Behavior
________________

This error may appear following an evolution in behavior, in previous versions. See `New in PHP 8.5, together with the ability to use first-class callable syntax inside constant expressions. <https://php-changed-behaviors.readthedocs.io/en/latest/behavior/New in PHP 8.5, together with the ability to use first-class callable syntax inside constant expressions..html>`_.