using Combinatorics

function myiterate(c::Combinatorics.Combinations, state = Int[min(c.t - 1, i) for i in 1:c.t])
    item = myiterate!(state, c.n, c.t)

    if item === nothing
        return nothing
    else
        return (item, state)
    end
end

function myiterate!(s::Vector{Int}, n::Int, t::Int)
    # item is return value, state is s

    if t == 0 	# special case to generate 1 result for t==0
    	if isempty(s)
    	    push!(s, 1)
    	    return Int[]
    	end
	return nothing
    end

    for i in t:-1:1
    	s[i] += 1
        s[i] > (n - t + i) && continue
        for j in i+1:t
            s[j] = s[j-1] + 1
        end
        break
    end

    s[1] > (n - t + 1) && return nothing
    return s
end

function test2(combs)
    x = 0
    next = myiterate(combs)
    while next !== nothing
    	item, state = next
        x += 1
        next = myiterate(combs, state)
    end
    x
end

@time test2(Combinatorics.Combinations(30, 12))
  1.747497 seconds (1 allocation: 160 bytes)