Why doesn't this code work? Related to Tuples and Types

General Usage
1

Here is an example:

mm(::Type{Tuple{X,Y}}) where X where Y = Type[X,Y]
julia> mm(Tuple{Int,T} where T<:Float64)
ERROR: UndefVarError: Y not defined
Stacktrace:
 [1] mm(::Type{Tuple{Int64,T} where T<:Float64}) at ./none:1
 [2] top-level scope at none:0

You can also try it with Base.unwrap_all, the result is same.

Thanks

2

You want

julia> (mm(::Type{Tuple{X,Y}}) where X where Y) = Type[X,Y]
mm (generic function with 1 method)

Nevermind, completely misread that.

3

what do you mean? that is no different from above.
It doesn’t work either.

4

Note the following:

julia> mm(::Type{Tuple{X,Y}}) where X where Y = :outer
mm (generic function with 3 methods)

julia> mm(::Type{Tuple{X,Y} where Y}) where X = :inner
mm (generic function with 3 methods)

julia> mm(::Type{Tuple{X,Y} where Y <: Float64}) where X = :specific
mm (generic function with 3 methods)

julia> mm(Tuple{Int,String})
:outer

julia> mm(Tuple{Int,T} where T<:Float64)
:specific

julia> mm(Tuple{Int,T} where T)
:inner

julia> mm(Tuple{Int,Float64})
:specific

I usually try not to do this kind of acrobatics and use some other, more transparent/readable mechanism, eg traits.