Cannot use dynamic method name in constant expression¶
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¶
<?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.
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..
