Early Return in Elixir

Damon Janis — Wed, 20 Oct 2021 12:29:51 +0000

The only thing I've missed while working in Elixir the last few years is an early return.

In Javascript, you can do this:

let contrivedFunction = arg => {
  if(!arg) {
    return 'falsy';
  }

  if([] !== []) {
    return 'wtf';
  };

  // This will never be evaluated because JS is
  // a sad language where [] does not equal []
  return 'truthy';
};

At any point, you can stop the execution of the current function and return a value, and nothing after that point will run.

Usually, in Elixir, you can get by just fine without that ability. You can use the with statement, pattern matching, or control flow like case and cond.

But sometimes, I really miss having an early return. Usually when I'm working in a really messy domain with a lethal combo of tech debt, third-party APIs, and a long chain of processing where things can go wrong in a lot of places.

I recently ran into a situation like that, and decided to do some digging. I knew that a function stopped execution as soon as an error was raised, so I thought I could maybe write a macro for that functionality. But then in the Elixir guides for try, catch, and rescue, I realized that the solution was hiding in plain sight:

def contrived_function(arg) do
  if !arg do
    throw("falsy")
  end

  if [] != [] do
    throw("wtf")
  end

  # Elixir is sane and [] does equal [], so this is possible
  "truthy"
catch
  value -> value
end

It turns out, when you throw within a function, execution stops and you can catch (and return) the value! No macros or extra abstractions needed.

I don't anticipate that I'll use this pattern very much - in most cases the standard methods of control flow are easier to reason about and follow.

But, I hope that like me you appreciate having an extra tool in hand for those situations when it feels like the best way to express a bit of logic.

DEV Community: Damon Janis

Early Return in Elixir