function many_loop(f, n)
    for i in 1:n
        f()
    end
end

f1_row(x, y) = hcat(x, y, x, y)
function f2_row(x, y)
    c = Matrix{Float64}(undef, 1, 4)
    @inbounds begin
        c[1] = x
        c[2] = y
        c[3] = x
        c[4] = y
    end
    return c
end

f1_col(x, y) = vcat(x, y, x, y)
function f2_col(x, y)
    c = Matrix{Float64}(undef, 4, 1)
    @inbounds begin
        c[1] = x
        c[2] = y
        c[3] = x
        c[4] = y
    end
    return c
end

f1_mat(x, y) = hvcat((2, 2), x, y, x, y)
function f2_mat(x, y)
    c = Matrix{Float64}(undef, 2, 2)
    @inbounds begin
        c[1] = x
        c[2] = x
        c[3] = y
        c[4] = y
    end
    return c
end


@assert vec(f1_row(0.3, 0.4)) == vec(f2_row(0.3, 0.4))
@assert vec(f1_col(0.3, 0.4)) == vec(f2_col(0.3, 0.4))
@assert f1_mat(0.3, 0.4) == f2_mat(0.3, 0.4)
many_loop(()->f1_row(0.3, 0.4), 1000000)

function f()
    x, y = rand(), rand()

    @info "row concatenation"
    @time many_loop(()->f1_row(x, y), 1000000)
    @time many_loop(()->f2_row(x, y), 1000000)

    @info "column concatenation"
    @time many_loop(()->f1_col(x, y), 1000000)
    @time many_loop(()->f2_col(x, y), 1000000)

    @info "matrix concatenation"
    @time many_loop(()->f1_mat(x, y), 1000000)
    @time many_loop(()->f2_mat(x, y), 1000000)
end

f()
using SparseArrays

@info "SparseArrays loaded"
f()