Transition to erlang v18 for erlang:now()

Example of a module using the macro provided

defmodule MyModule do
   require Now
   use Bitwise, only_operators: true
   # generates a prefix based on system time
   def gen_prefix do
     Now.system_time() &&& 281474976710655
   end
end

• Now.timestamp -> :erlang.timestamp in v18 and :erlang.now before

• Now.system_time -> :erlang.system_time in v18 and a conversion of the triple tuple of :erlang.now converted in ms.

Warning: although :erlang.timestamp has the same format as :erlang.now it is not equivalent, see Find out more

Rationale

This project is an atempt to answer question posted here on stackoverflow

This issue

:erlang.now() is deprecated in v18, how to make a smooth transition.

Sample code before v18:

defmodule MyModule_v17 do
  use Bitwise, only_operators: true
  def gen_trans_prefix do
    {gs, s, ms} = :erlang.now
    (gs * 1000000000000 + s * 1000000 + ms) &&& 281474976710655
  end
end
best I came up with:

First fix attempt:

defmodule MyModule_v18 do
  use Bitwise, only_operators: true
  Kernel.if Keyword.get(:erlang.module_info, :exports) |> Enum.any?(fn({:system_time, 1}) -> true; (_) -> false end) do
    def gen_trans_prefix do
      :erlang.system_time(:micro_seconds) &&& 281474976710655
    end
  else
    def gen_trans_prefix do
      {gs, s, ms} = :erlang.now
      (gs * 1000000000000 + s * 1000000 + ms) &&& 281474976710655
    end
  end
end

Better fix:

define erlc_options in mix and use it in MyModule

this is based on input from @potatosalad and jose project

Find out more

This is already covered in the "Time and Time Correction in Erlang" documentation and also in the "Time Goes On" postscript to the wonderful "Learn You Some Erlang" book. as suggested by Steve Vinoski