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twiss • last Sunday at 11:33 PM • 2 replies • view on HN

I may be missing something about how the PHP compiler/interpreter works, but I don't quite understand why this is apparently feasible to implement:

    class BlogPostRepository extends BaseRepository<BlogPost> { ... }
    $repo = new BlogPostRepository();
but the following would be very hard:

    $repo = new Repository<BlogPost>();
They write that the latter would need runtime support, instead of only compile time support. But why couldn't the latter be (compile time) syntactic sugar for the former, so to speak?

(As long as you don't allow the generic parameter to be dynamic / unknown at compile time, of course.)

Replies

jasone • last Monday at 12:19 AM

The former merely exposes a `BlogPostRepository` class. The latter requires some mechanism for creating a generic object of concrete type, which is a lot bigger change to the implementation. Does each parametrized generic type have its own implementation? Or does each object have sufficient RTTI to dynamically dispatch? And what are the implications for module API data structures? Etc. In other words, this limitation avoids tremendously disruptive implementation impacts. Not pretty, but we're talking PHP here anyway. ;-)

baobun • last Monday at 4:24 AM

Usually you are right. I assume the inability to sugar would be that "because PHP", the value/type of BlogPost can not be derived at compile-time?