Julia

speed.jl

x = {[1:100]...}

function f1(X)
	T = None
    for x in X
        T = promote_type(T,typeof(x))
    end
    return T
end

function f2(X)
	T = promote_type(map(typeof,X)...)
	return T
end

function f3(X)
	T = reduce((acc, x) -> promote_type(acc, typeof(x)), None, X)
	return T
end

inner(acc, x) = promote_type(acc, typeof(x))
function f4(X)
	T = reduce(inner, None, X)
	return T
end

num_iter = 1000

f1(x)
f2(x)
f3(x)
f4(x)

println("f1")
@time for i in 1:num_iter
   f1(x)
end

println("f2")
@time for i in 1:num_iter
   f2(x)
end

println("f3")
@time for i in 1:num_iter
   f3(x)
end

println("f4")
@time for i in 1:num_iter
   f4(x)
end