List - get first item

Prepare lists

lists = [
  [],
  [nil],
  [1],
  [1, 2],
  [1, 2, 3]
]

[[], [nil], [1], [1, 2], [1, 2, 3]]

Prepare test function

test_fun = fn do_test ->
  for list <- lists do
    try do
      do_test.(list)
    rescue
      e -> inspect(e)
    end
  end
end

#Function<42.125776118/1 in :erl_eval.expr/6>

hd

test_fun.(fn list ->
  hd(list)
end)

["%ArgumentError{message: \"errors were found at the given arguments:\\n\\n  * 1st argument: not a nonempty list\\n\"}",
 nil, 1, 1, 1]

List.first/1

test_fun.(fn list ->
  List.first(list)
end)

[nil, nil, 1, 1, 1]

Enum.fetch/2

test_fun.(fn list ->
  Enum.fetch(list, 0)
end)

[:error, {:ok, nil}, {:ok, 1}, {:ok, 1}, {:ok, 1}]

Enum.fetch!/2

test_fun.(fn list ->
  Enum.fetch!(list, 0)
end)

["%Enum.OutOfBoundsError{message: \"out of bounds error\"}", nil, 1, 1, 1]

[first | _rest]

test_fun.(fn list ->
  [first | _rest] = list
  first
end)

["%MatchError{term: []}", nil, 1, 1, 1]

[first, , ]

test_fun.(fn list ->
  [first, _, _] = list
  first
end)

["%MatchError{term: []}", "%MatchError{term: [nil]}", "%MatchError{term: [1]}",
 "%MatchError{term: [1, 2]}", 1]

Enum.at/2

test_fun.(fn list ->
  Enum.at(list, 0)
end)

[nil, nil, 1, 1, 1]