Compute supertype parameters

[Oblynx]

I experimented with the following behavior, which is not supported by this package:

struct CustomArray{N1,N2} <: AbstractArray{Int, N1+N2}
  ...
end

The intent is to define 2 different kinds of dimensions for the array, which have a semantic difference. There is of course the same workaround of explicitly passing the expression N1+N2 as a 3rd type parameter.

Please consider this as a feature request, if this use case is convincing.

[vtjnash]

Sure, that’s well in line with what this package already does, and just needs to be added to the syntax rules.

[richardreeve]

On a related note, I’d really like to be able to do this:

abstract type SuperT{A} end
@computed struct SubT{B} <: SuperT{f(B)}
  b::B
end

At the moment this errors as f is not defined, or works incorrectly with existing functions like eltype since eltype is defined on Any...

[wsshin]

Another related capability I would like:

@computed struct MyType{N,V<:AbstractArray{N+2}}
    a::V
end