When to use: Case vs if

I think that if works great for boolean conditions and it’s often used in the Elixir’s codebase. I’d say that case with just true/false feels weird.

I pretty much feel the same way you do.

I think if/2 is a good fit when you have:

• no other nested ifs under it,
• when you check for truthy/false values.

Other than that I prefer to use case and cond. cond is particularly useful for replacing nested ifs or if/elseifs.

Thanks for the responses. I was worried I was overusing it from a style perspective but this all makes sense.

I experienced this in a Credo report today:

Refactoring opportunities
┃ [F] → Cond statements should contain at least two conditions besides `true`,
┃           consider using `if`  instead.

Not convinced by this rules

I was doing LeetCode and was solving a problem by reducing an enumerable, where the reducer does different things to the accumulator based on whether a condition is true or false.

I didn’t think much about the difference between if-else and case. So I did this:

case MapSet.member?(acc, item) do
  true -> {:halt, true}
  false -> {:cont, MapSet.put(acc, item)}
end

And the runtime was 655 ms, better than 25% solutions.

I tried using if instead, the runtime was 525 ms, that is 100 ms shorter and better than 100% solutions.

In conclusion, if you are only dealing with true or false, if-else is definitely faster.

Yeah absolutely doesn’t make any sense. case is an erlang construct that is considered a core operation, while if is a syntactic sugar (AKA macro) that uses case under the hood, you can inspect the source code yourself.

More than that if does more work: it’s checking falsiness.

But I still use if. Usually your conditionals are not bottlenecks and it’s easier to read.

Absolutely, however I would strongly recommend to read this topic: https://forum.elixirforum.com/t/my-thoughts-on-the-if-statement/61985 .

There is a clear intent difference between using case with true/false and if.

Thanks for sharing! I didn’t know that until now. (This is mental!)

I’m reading the source code and saw optimize_boolean, tbh I have zero idea what this is. Is it this what makes if slightly faster?

My assumption is this is a compile-time optimization, for example you have the following case:

a = true

if a == true do
...
end

This statement can be evaluated at compile-time, hence there is no need to execute the case statement.

In your case, if that is the case, then you literally can optimize if out of your codebase, so it makes no sense in benchmarking if vs case.