> I think before rust, language designers mixed up the various properties these values can have. As a result, many incomprehensible designs were the result. rust models the most important memory-related properties through its two call conventions (passing or borrowing). And Hylo moves even more properties into the call conventions. Namely, Hylo uses the keywords let, set, sink, and inout. This way Hylo additionally represents e.g. initialization (rust models this with a separate type).

Is anyone able to clarify what's meant by "initialization" here and what "separate type" Rust uses for this (e.g. something defined specifically for each type getting passed this way, or a generic warpper type in the standard library)? Offhand, my understanding is that three of the Hylo keywords listed correspond to passing by ownership, shared reference, or mutable reference in Rust, and whichever doesn't correspond to one of those is something that a separate type if used for in Rust, but I'm not confident that my understanding is correct because the only thing I can think of that might be related to "initialization" is constructors, which Rust notably does _not_ have any formal concept of in the language, since functions that return types are just like any other function implemented on a type without a self parameter.

I'm also not completely sure what the intended distinction is being made between whatever separate type is and references in Rust, since a reference is also a separate type than the type of the value of references. I could imagine someone might think that references are different than user-defined types in a way that other standard library types like Box and Arc aren't, but I'd argue that the unique syntax that references have is actually not that significant, and semantically being located inside std makes them far closer to references in terms of potentially behaving in special ways due to them having access to certain unstable APIs around things like allocations and fact that std is developed in tandem with the compiler, which leaves the door open for those types to take advantage of any additional internal APIs that get added in the future.