Concatenate Generators

[DNF]

function foo(N)
    a = Vector{Int64}(undef, 2N)
    a[1:N] .= 0
    a[N+1:end] .= 1
    return a
end

# or, a little bit slower

function bar(N)
    a = zeros(Int, 2N)
    a[N+1:end] .= 1
    return a
end