output.txt

iex(2)> Test.test1
{1474377, :ok}
iex(3)> Test.test2
{755840, :ok}

test.ex

defmodule Test do
	defp regexp(url) do
		if String.match? url, ~r/^hello, / do
			url <> "world"
		else
			url
		end
	end
	defp better(url) do
		case String.downcase(url) do
			<<"hello, "::utf8, _::binary>> -> url <> "world"
			_ -> url
		end
	end

	def test1 do
		:timer.tc fn ->
			Enum.each 1..1000000, fn _ -> regexp("hello, ") end
		end
	end
	def test2 do
		:timer.tc fn ->
			Enum.each 1..1000000, fn _ -> better("hello, ") end
		end
	end
end

Awesome! :)

Hope it will convince you to merge the pull request before 0.12.4 available:)