If you're interested about generics in PHP, you can read this blog post by the PHP foundation: https://thephp.foundation/blog/2024/08/19/state-of-generics-... or this PR by Nikita: https://github.com/PHPGenerics/php-generics-rfc/issues/45.

TLDR: The PHP compiler isn't really suited for the job, it would introduce a lot of complexity to an already complex codebase and the memory/performance hit would be substantial.