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Comment by actionfromafar | Hacker News Reader

Ok, that was harsh, but I was excited and wanted to get to the meat of the article but then it just ended.

I was thinking, "that's not how I would design a C++ interface". I still don't understand what these Rust types are good for, but I want to know.

I miss how in Ada you can define which values an int can have. Can you do that in Rust?

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> I miss how in Ada you can define which values an int can have. Can you do that in Rust?

yes, kind of: https://crates.io/crates/deranged

It'll take another while until const generics on stable are advanced enough to make this properly usable, such that e.g. `RangedU32<3, 10> + RangedU32<5, 6> = RangedU32<8, 16>`.

You're looking for dependent types and while Rust has a limited form, it doesn't have them fully. Idris does, on the other hand.

Yeah there’s a serious lack of discussion of Idris in this thread. Probably the most fun, least used programming language ever.

You can do with a sum type (enum) that is represented by a u32 (repr(u32)), or converts into one. Though I don’t know Ada so can’t speak to how accurately I’m creating the analogy.

In Ada/Pascal/Modula-2/Modula-3/.... it would be something like,

    type
      Subrange = 56..100;
      Colors = (Red, Green, Blue);
      Pixel = array [Colors] of byte;

With the plus that it is a compiler error if an invalid value is assigned, and can be validated at compile time (or it will be a range runtime error otherwise).

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