array of array promotion

[StefanKarpinski]

Intersting promotion example here: https://discourse.julialang.org/t/what-on-earth-does-any-do/7625/5. In short, this is good:

julia> [ [1, 2, 3], [1, 0.5, 0.25, 0.125], [-1, -2] ]
3-element Array{Array{Float64,1},1}:
 [1.0, 2.0, 3.0]
 [1.0, 0.5, 0.25, 0.125]
 [-1.0, -2.0]

But this is less good:

julia> [ [1, 2, 3], ["1", "2", "3"], [1.0, 2.0, 3.0] ]
3-element Array{Array{Any,1},1}:
 Any[1, 2, 3]
 Any["1", "2", "3"]
 Any[1.0, 2.0, 3.0]

Perhaps array promotion should not try to convert all arrays to the same element type unless that element type is concrete.

[Liso77]

IMHO explicit is better than implicit also in this case.
So rather than:

julia> repr(Any[ [1, 2, 3], [1, 0.5, 0.25, 0.125], [-1, -2] ])
"Any[[1, 2, 3], [1.0, 0.5, 0.25, 0.125], [-1, -2]]"

julia> repr([ [1, 2, 3], [1, 0.5, 0.25, 0.125], [-1, -2] ])
"Array{Float64,1}[[1.0, 2.0, 3.0], [1.0, 0.5, 0.25, 0.125], [-1.0, -2.0]]"

I like to see:

julia> repr([ [1, 2, 3], [1, 0.5, 0.25, 0.125], [-1, -2] ])
"[[1, 2, 3], [1.0, 0.5, 0.25, 0.125], [-1, -2]]"

julia> repr(Array{Float64,1}[ [1, 2, 3], [1, 0.5, 0.25, 0.125], [-1, -2] ])
"Array{Float64,1}[[1.0, 2.0, 3.0], [1.0, 0.5, 0.25, 0.125], [-1.0, -2.0]]"

[JeffBezanson]

Wasn't this already changed by #22757?

julia> [ [1, 2, 3], ["1", "2", "3"], [1.0, 2.0, 3.0] ]
3-element Array{Array{T,1} where T,1}:
 [1, 2, 3]      
 ["1", "2", "3"]
 [1.0, 2.0, 3.0]

[vtjnash]

Looms like it. That’s what I was expecting to need to implement. @StefanKarpinski what’s up with you example not matching Jeff’s result?

[StefanKarpinski]

My mistake! I must have run the example in a 0.6 session – I've been running 0.6 for Pkg3 for a while.