broadcasting getindexwith colon unexpected

[KlausC]

Is the following intended or a bug?
I was surprised, because changing 1:4 to : changed the output type. I expected to see the same vector of vectors in both cases.

julia> v
2×4 Array{Complex{Float64},2}:
     -1.0+0.0im   0.739183+0.196401im   0.739183-0.196401im  0.627138+0.0im
 0.821812+0.0im  -0.501408+0.375337im  -0.501408-0.375337im       1.0+0.0im

julia> getindex.(Ref(v), Ref(:), 1:4)
4-element Array{Array{Complex{Float64},1},1}:
 [-1.0 + 0.0im, 0.8218121719277804 + 0.0im]                                             
 [0.7391830349599989 + 0.1964008799517751im, -0.501407601380187 + 0.37533731526626024im]
 [0.7391830349599989 - 0.1964008799517751im, -0.501407601380187 - 0.37533731526626024im]
 [0.6271384123034096 + 0.0im, 1.0 + 0.0im]                                              

julia> getindex.(Ref(v), Ref(:), :)
2×4 Array{Complex{Float64},2}:
     -1.0+0.0im   0.739183+0.196401im   0.739183-0.196401im  0.627138+0.0im
 0.821812+0.0im  -0.501408+0.375337im  -0.501408-0.375337im       1.0+0.0im

julia> 

[GunnarFarneback]

The broadcast machinery effectively expands

getindex.(Ref(v), Ref(:), 1:4)

to

[getindex(v, :, 1), getindex(v, :, 2), getindex(v, :, 3), getindex(v, :, 4)]

or equivalently

[v[:, 1], v[:, 2], v[:, 3], v[:, 4]]

since 1:4 is iterable.

For

getindex.(Ref(v), Ref(:), :)

all arguments are scalars (: is just a generic function and Ref(:) doesn't make a difference) so it expands to

getindex(v, :, :)

i.e. v[:, :].

The key observation is that : only can be interpreted as "all indices" within the context of the getindex function. The broadcast machinery is fully generic and doesn't try to guess how some specific function like getindex will interpret its arguments.

[mbauman]

Duplicate of #30450