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Date: Sun, 02 Feb 2025 14:38:32 +0100
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Subject: Re: [PHP-DEV] RFC: First Class Callables in constant expressions
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From: tim@bastelstu.be (=?UTF-8?Q?Tim_D=C3=BCsterhus?=)

Hi

Am 2025-01-31 23:36, schrieb Larry Garfield:
> Purely out of curiosity and for educational value, what was so 
> complicated about it?  I would have expected it to be straightforward.

FCC internally are effectively treated as function calls with a funny 
parameter list. This means that all valid ways to perform a function 
call are valid ways to create a FCC. And likewise do all constraints of 
a function call also apply to creating a function call. FCCs in 
const-expr need to replicate those semantics as applicable. For us this 
means: A FCC in a parameter default value behaves, as if the assignment 
was the first line in the function body. Likewise must a FCC in a 
property default value behave as if it was assigned in the first line of 
the constructor body.

And then amongst others you have the following (edge-)cases to take into 
account:

- All kinds of expressions can be used as a function name (this RFC 
excludes those for simplicity).
- A FCC can resolve to a dynamic function when __call() or 
__callStatic() is implemented (this RFC excludes those for simplicity).
- Static methods can directly be called on a trait (this is deprecated, 
but supported by the RFC).
- Calls to free-standing functions need to take the global namespace 
fallback into account (which will be cached for each individual call, 
which has funny effects when the function in the same namespace gets 
defined after some of the calls already executed at least once).
- Visibility and names needs to be resolved correctly, including 
references to `self` and `static`.

For regular closures (i.e. the first RFC) it was as simple as: Disallow 
`use` and require `static` and you're done. They are much less 
context-dependent.

Best regards
Tim Düsterhus