supertypes(T) function?

[stevengj]

When trying to understand (or explain) a type T, I often find myself typing supertype(T), supertype(supertype(T)), supertype(supertype(supertype(T))), etcetera in order to see the type hierarchy. This is tedious and annoying. It would be nice to have a function supertypes(T) that just returned a tuple of T and all its supertypes, e.g.

julia> supertypes(Int)
(Int64, Signed, Integer, Real, Number, Any)

Sample implementation:

function supertypes(T::Type)
    S = supertype(T)
    return S === T ? (T,) : (T, supertypes(S)...)
end

It could be made to execute completely statically (e.g. is adding @pure enough?).

[JeffBezanson]

Sounds fine to me. I think it could return a Vector{Any} like subtypes; is there a real use case for evaluating it at compile time?

[StefanKarpinski]

What about just adding supertype(T, n::Integer=1) to get the nth supertype? Perhaps both.

[stevengj]

I guess my feeling is that since it can be static, it should be static (or at least return a tuple type that could be computed statically in a future version), since we can’t change our minds and make it static later if we return an array.

In contrast, the subtypes function cannot be static.