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elixirphoenix-frameworkelixir-mix

Is it possible in Elixir to have code conditionally present depending on Mix environment?

Basically like #ifdef/#else/#endif in C/C++ I want some code top be present during mix test and removed in production, so I don't need to test for Mix.env == :test in a piece of code that is very often called.

I know it's considered bad practice, but is it possible and how?

Solution

  • While building a release, Mix is available. In the release itself, it is not. If you are positive you want the code to be stripped out from the release version, use a macro:

    defmodule StrippedInRelease do
  defmacro fun(do: block) do
    if Mix.env == :test do
      block # AST as by quote do: unquote(block)
    end
  end
end

    and use it like:

    require StrippedInRelease
StrippedInRelease.fun do
  def yo, do: IO.puts "¡yo!"
end

    It is to be expanded during a compilation time and, hence, everything passed as a block will be defined in the :test environment and stripped out in other environments.