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0 pointsori_b12y ago0 comments

Personally, I think it would be better if interfaces were explicit, but the list of interfaces on a type was open, allowing you to add interfaces over any type anywhere, and not just in the place where the type is defined.

    type foo = ...

and

    impl hashable(foo) = ...
    impl hashable(int) = ... // yep, adding to a builtin type

This is the way that Myrddin currently handles it.

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2 comments · 1 top-level

eridius12y ago· 1 in thread

This is similar to how Rust works. You can implement new traits (which are what Rust calls interfaces) on pre-existing types. The rule is that either the trait or the type must be defined in the current crate (e.g. in the current library).

This means that my library can define a new trait and implement it on, say, int. Or I can define a new type and implement a pre-existing trait on it. But it prevents me from implementing pre-existing traits on pre-existing types, which is important for the compiler to be able to answer the question "does type A implement trait B" without having the answer change when a new library is linked.

ori_bOP12y ago

I do not have that restriction; Traits are instead scoped by module, so a trait implementation in one module is not necessarily available in another, unless it is exported explicitly. Now, on the other hand, I doubt Rust has the same kind of bugginess I have :)

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