Metaprogramming in Elixir/

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Avoiding Common Pitfalls

Avoiding Common Pitfalls

Let's learn a few common mistakes that we should always avoid.

We'll cover the following...

Elixir is a powerful tool, but you’ll need to be careful.There are a few common mistakes that can wreak havoc on our codebase over time if ignored. Let’s find out ways to avoid getting caught in the web of code generation.

Don’t rely on use

One of the most common mistakes newly minted meta-programmers make is treating use as a way to mix in functions from other modules. This tempting idea conflates the concept of a mix-in from other languages, where we can introduce methods and functions from one module into another. In Elixir, this pitfall looks something like this: Consider a StringTransforms module that defines a number of string transformation functions to use around our codebase. We might write something like this for easy sharing across different modules:

defmodule StringTransforms do
  defmacro __using__(_opts) do 
    quote do
      def title_case(str) do
        str
        |> String.split(" ")
        |> Enum.map(fn <<first::utf8, rest::binary>> ->
          String.upcase(List.to_string([first])) <> rest
        end)
        |> Enum.join(" ")
      end

      def dash_case(str) do
        str
        |> String.downcase
        |> String.replace(~r/[^\w]/, "-")
      end
      # ... hundreds of more lines of string transform functions
    end
  end
end

defmodule User do
  use StringTransforms 

  def friendly_id(user) do
    dash_case(user.name)   
  end
end
`StringTransforms` module that defines a number of string transformation functions

Execute the following commands to run the code:

iex> c "String_Transforms.exs"
iex> User.friendly_id(%{name: "Elixir Lang"}) 
# Output: "elixir-lang"

On line 2, we define a using macro to house a quoted expression of some ...