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Date: Tue, 20 Feb 2024 20:35:18 +0000
To: PHP internals <internals@lists.php.net>
Subject: [PHP-DEV] Resolving self and parent types at compile time
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From: internals@gpb.moe ("Gina P. Banyard")

Hello internals,

I have an outstanding PR where I implemented resolution of the parent and s=
elf types at compile time. [1]

The reasoning for this is to attempt to add various methods to ReflectionTy=
pe, such as isCovariant/isContravariant and other type relation methods.
Currently, we cannot do this easily, as we need a "scope" with the Reflecti=
onType to resolve the relative class types self, parent, and static.

The current implementation uses two new bit flags to mark the type as self =
and parent, to be able to preserve BC with existing code relying on the nam=
es self/parent.
However, we are limited in flag numbers available and using two bits for th=
is seems wasteful.

The question: Is it an issue if the self and parent types are resolved at c=
ompile time? (when possible)

In its simplest form, this would affect error messages (such as type errors=
) and also the compile time type redundancy check. [2]

Note: traits and unbound Closures would still require a way to provide the =
"scope" but those seem to be cases of limited use for analysing/comparing R=
eflectionTypes.

Best regards,

Gina P. Banyard

[1] https://github.com/php/php-src/pull/11460
[2] If a class Foo declares a method with union type Foo|self no compile ti=
me error is thrown at the moment, this would change as self would correspon=
d to Foo and the type would be Foo|Foo which is redundant