Parametrized structs with traits

[AriMKatz]

What do you think about a macro that allows defining a structs parametrized on traits instead of subtypes?

Can the compiler be made to specialize the same way as using subtypes?

[schlichtanders]

can you give an example, please?

[AriMKatz]

Sure.

We have this example from the manual:

struct Rational{T<:Integer} <: Real
    num::T
    den::T
end

Instead we can have:

@trait struct Rational{numberness(T)<:IntegerLike} <: Real
    num::T
    den::T
end

I don't have a specific use case for this at the moment, but it would be cool for traits to have broader utility.

Related: https://github.com/vtjnash/ComputedFieldTypes.jl and https://github.com/JuliaLang/julia/issues/18466

[schlichtanders]

Interesting case. I haven't yet thought about this and don't know the details how it is implemented in Julia.

But on a first sight, something like this should be possible, as in the end also the existing Rational struct just offers itself as a couple of functions with which you can construct that struct.

For sure there will be edge cases, but I can imagine that you can overwrite the constructer functions such that the checks are properly done.

Very interesting suggestion.