Why `Tuple{Vararg{T, 2} where T} == Tuple{Any, Any}`?

General Usage
1

Why this is the case, instead of being a UnionAll like Arrays?

2

Tuples are covariant as opposed to all other parametric types that are invariant.
The reason for this is that tuples are used in signature matching in method dispatch, see https://docs.julialang.org/en/latest/manual/types/#Tuple-Types-1.

Here is an example of this distinction:

julia> Tuple{Int} <: Tuple{Any}
true

julia> Vector{Int} <: Vector{Any}
false

julia> Vector{Int} <: Vector{<:Any}
true

You might also check out an answer on StackOverflow that I have just written on a related topic.

5 Likes
3

I was thinking in the same direction too. I managed to convince myself after testing:

Union{Tuple{Int}, {Tuple{Any}} == Tuple{Any}