Stupid Doc Tricks In Elixir

So last night we had our first Detroit Erlang/Elixir meetup and as part of it I wanted to do a little coding exercise to help people to get their feet wet with Erlang and/or Elixir, as they chose.  We simply worked through FizzBuzz and we came up with two different Elixir solutions and two different Erlang solutions. I never stop being surprised by developer creativity.

That said, I keep striving to improve the code I write and striving to use the tools that the language provides me.  Elixir has module attributes and it’s also got module documentation as a first class citizen in the language.  So I thought to myself why not extend my simple fizzbuzz code a bit to use these two features–to better learn how to use them.  Here’s the code such as it is:


defmodule FizzBuzz do
@fizz 3
@fizzmsg "Fizz"
@buzz 5
@buzzmsg "Buzz"

@moduledoc "
Ye olde FizzBuzz test in all of its glory.
If the number is a multiple of #{@fizz} then print #{@fizzmsg}.
If the number is a multiple of #{@buzz} then print #{@buzzmsg}.
If it's a multiple of both then print #{@fizzmsg<>@buzzmsg}.
Else print the number itself.

Example usage:
iex> for i <- 1..100, do: FizzBuzz.getFB(i)
1
2
#{@fizzmsg}
4
#{@buzzmsg}
"

  def getFB(n) do
    cond do
      rem(n,@fizz) == 0 and rem(n,@buzz) == 0 ->
        IO.puts @fizzmsg <> @buzzmsg
      rem(n,@fizz) == 0 ->
        IO.puts @fizzmsg
      rem(n,@buzz) == 0 ->
        IO.puts @buzzmsg
      true ->
        IO.puts "#{n}"
    end
  end
end

Now the code itself isn’t anything very special.  But the module attributes and the fact that I can avoid specifying magic numbers is just awesome.  What if I wanted to change the code to print “Argh!” on 3 instead of “Fizz”?  Of course were I to change the number for “Fizz” then I would need to make more extensive changes but this does cover one common type of change. With the code set up in this way, I only need to change things in one place and my docs will be updated as well as my code.

I know this is sort of a “Stupid Doc Trick” but it still seemed worth sharing with others.  The idea of only needing to change a constant in one place and having everything else update is a very appealing one.

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