Different/simple ways to implement some_function() and some_function!() that raises exception

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6

I think there is some interesting thought here. I certainly have written my fair share of bang-functions using the case-approach. And while I have no objection in particular against it (it’s only 4 lines after all) this could be a nice little macro exercise.

Disclaimer: As @al2o3cr writes below, using this is probably not a good idea, as it’s a major layer of indirection which will make your codebase harder to reason about. Nevertheless it’s an interesting use-case for macros, so consider this an educational example rather than a production ready one.

defmodule Boom do
  defmacro defbang({name, _meta, args}, raising: error) do
    quote do
      def unquote(:"#{name}!")(unquote_splicing(args)) do
        case apply(__MODULE__, unquote(name), unquote(args)) do
          {:ok, value} -> value
          {:error, reason} -> raise unquote(error), reason
        end
      end
    end
  end
end

Which you could then use like this:

defmodule Test do
  import Boom

  def test(nil), do: {:error, "is nil"}
  def test(val), do: {:ok, val}

  defbang test(num), raising: ArgumentError
end

Test.test(42)
#=> {:ok, 42}

Test.test("test")
#=> {:ok, "test"}

Test.test(nil)
#=> {:error, "is nil"}

Test.test!(42)
#=> 42

Test.test!("test")
#=> "test"

Test.test!(nil)
#=> ** (ArgumentError) is nil

As mentioned before, I’m not saying that this is a good idea - after all it’s a probably unnecessary layer of indirection - but it’s possible.