`hcat(A, B)` is SArray, but `[ A ;; B]` is not

[dev10110]

Hi,

consider this MWE:

using LinearAlgebra, StaticArrays

A = @SMatrix randn(3, 4)
B = @SMatrix randn(3, 2)

as expected,

hcat(A, B)  #returns 3×6 SMatrix{3, 6, Float64, 18}

but

[ A ;; B]  # returns 3×6 Matrix{Float64}

If we compare this to vcat,

A = @SMatrix randn(3, 4)
B = @SMatrix randn(2, 4)
vcat(A, B) # returns 5×4 SMatrix{5, 4, Float64, 20} (as expected)
[ A ; B] # returns 5×4 SMatrix{5, 4, Float64, 20} (as expected)

So somehow, the array concatenation works for vcat but not for hcat.

Is this expected behavior?

[mcabbott]

array concatenation works for vcat but not for hcat

I think the problem is hvncat, while hcat and vcat are both fine:

julia> [A  B] isa SMatrix
true

julia> Meta.@lower [A  B]
:($(Expr(:thunk, CodeInfo(
1 ─ %1 =   dynamic Base.hcat(Main.A, Main.B)
└──      return %1
))))

julia> [A ;; B] isa Matrix
true

julia> Meta.@lower [A ;; B]
:($(Expr(:thunk, CodeInfo(
1 ─ %1 =   dynamic Base.hvncat(2, Main.A, Main.B)
└──      return %1
))))

julia> [A ;; B] == [A B] == hcat(A, B)
true

Nearly a duplicate of #1262, which is about hvcat.