.. _cannot-use-dynamic-method-name-in-constant-expression:

Cannot use dynamic method name in constant expression
-----------------------------------------------------
 
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Description
___________
 
PHP 8.5 allows first-class callable syntax (``(...)``) to be used inside a constant expression -- a global constant, a class constant, a static property default, a parameter default value, and so on -- so that a static method can be turned into a ``Closure`` at compile time.

To build that closure, the method name must be resolvable at compile time. Here, the braced expression ``{[1, 2]}`` is not a simple, literal method name: it is an array, which cannot represent a method name at all. Since the compiler cannot fold it down to a plain string, it reports that a dynamic name was used.

This check only applies to static method calls (``X::method(...)``); the equivalent restriction for a plain function name is reported as 'Cannot use dynamic function name in constant expression'. When the braced expression does resolve to a scalar value that simply is not a legal method name (such as an integer), PHP reports 'Illegal method name' instead.

Example
_______

.. code-block:: php

   <?php
   
   class X {
       public static function foo() { return 1; }
   }
   
   const C = X::{[1, 2]}(...);
   
   var_dump(C);
   
   ?>

Solutions
_________

+ Use a literal string for the method name.
+ Move the closure creation out of the constant expression, into ordinary code, where dynamic method names are allowed.

Related Error Messages
______________________

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

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>`_.