Rust stabilizes generic associated types

Re:Rust stabilizes generic associated types by whatshisface on Tuesday September 13, 2022 @05:08PM (#32830205)

GATs are a really straightforward extension of what the language already has. All this means is that now a generic type can take a value as a parameter, for example there could be a generic fixed-length array, which took a length as a parameter. In the past libraries had to hack their way around this by having huge tables of types named like, "N1, N2... N16... N1003", which were passed to generic signatures to indicate to the type system how big something had to be.

I don't think this makes the language more confusing, because putting an integer inside of the generics brackets is something that previously you might try to do, if you didn't know it wasn't allowed. In fact, I would go so far as to say that this is a compiler feature, rather than a language feature, because it fills in a semantic hole that already existed in the way Rust programmers thought about Rust types. :-)

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Re:Rust stabilizes generic associated types by petrosagg on Tuesday September 13, 2022 @05:15PM (#32830267)

The feature you're referring to is const generics which is different than generic associated types (GATs) which is the feature being stabilized.

min_const_generics have been on stable for while

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Re:Rust stabilizes generic associated types by tialaramex on Tuesday September 13, 2022 @06:21PM (#32830913)

Note however broader Const Generics, allowing you to use your enumerated Hat type as a constant parameter to a type, producing PigInAHat<Hat::StrawBoater> as a distinct type from PigInAHat<Hat::Top> are not yet in stable Rust and aren't on the near horizon.

The idea is that any types which Rust can see for itself can be trivially compared for equality will eventually qualify for this purpose, so your Hat enumeration, or a structure with four integers and a boolean in it, or anything that Rust says "Yeah, I'll just memcmp that for equality" would qualify. No floating point numbers, no strings, nothing actually crazy. But this is in some undefined future, for now we just have min_const_generics which is basically the fundamental integral types as constants in generics.

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