Using List.first instead of Enum.at(0)

The docs for the List module states it works only on lists whereas the Enum module works on anything that implements the Enumerable protocol. Additionally, the List module docs recommends using the Enum module.

This comes directly from the List docs:

Specialized functions that only work on lists.

In general, favor using the Enum API instead of List.

I’d probably go with using Enum in general. I have never found myself reaching for an API available in List in the past year of my Elixir development.

Also see that the implementation of List.first is very simple:

def first(), do: nil
def first([h | _]), do: h

from elixir/lib/elixir/lib/list.ex at v1.3.4 · elixir-lang/elixir · GitHub

I usually use Enum.take/2

I started wondering if one should prefer either Enum.take/2 or Enum.at/3 when I realized that what I usually want is Enum.head/1. That started me thinking that the the more functional approach is pattern matching [ head | tail ].

I (re-)learn something new every day.

I just use hd.

The difference is that, for an empty list, List.first/1 and Enum.at/2 will return nil and hd and pattern matching will raise an error.

Depends on how strict you want to be. Should it really be a list with a first element or not?

FWIW I literally never use Enum.at. Lists are the only thing I end up using on a regularly basis where “first” actually means something. That is, I’m not sure why I would ever call Enum.at(0) on a map. Given that looking at a list, List.first is just more semantically clear.

I have to second @benwilson512 here, I also almost never use Enum.at/1.

On my side I like to use hd because it’s very short, but I agree that it applies only to Lists.

There’s a big difference between hd and List.first however. [] |> hd blows up. [] |> List.first is nil. I almost never use hd because I can generally just pattern match when I expect there will be one thing. List.first is handy when I either want the first thing or nil if there isn’t any.