Specialize on trait

As far as I can tell, the following will not compile:

trait T1:
    pass

trait T2:
    pass

struct S[T: T1]:
    pass

struct S[T: T2]:
    pass

trait T1:
    pass

trait T2:
    pass

struct S[T: T1]:
    pass

struct S[T: T2]:
    pass

Is the intention to allow this sort of type specialization in the future? I have a workaround using static methods for compile-time branching. However, it requires the definition of a trait that is the superset of the two cases and so each has to fulfill functions that the (sub-)trait does not require.

3 Replies

benny•3mo ago

conditional conformance is coming down the pipeline and is available in nightly, the way you could kind of achieve this is parameterizing the struct with T as AnyType (or Variant[S1, S2]) then having specific functions require Self[S1] etc look more in #nightly if this seems like the direction you want to go

benny•3mo ago

trait A:
    ...

trait B:
    ...

struct Generic[T: AnyType]:
    fn any(self):
        ...

    fn requires_a(self: Self[A]):
        ...
    
    fn requires_b(self: Self[B]):
        ...

trait A:
    ...

trait B:
    ...

struct Generic[T: AnyType]:
    fn any(self):
        ...

    fn requires_a(self: Self[A]):
        ...
    
    fn requires_b(self: Self[B]):
        ...

@tkeitt

tkeitt•3mo ago

Thanks. I found it in the changelog. But your example is clearer.

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Specialize on trait