The usual rule of thumb is to go from the more specific, to the more generic…

Of course for each rule You can find exception

It may also be helpful to clarify that maps, unlike lists, allow for partial matches, so:

%{num: num} = %{num: 1, acc: 5} # Match!
[a, b, c] = [1, 2, 3, 4] # No match!

Another option is to consider 1 as a default value of acc and then you can do it with a single function clause

def test1(%{num: num} = m), do: num + Map.get(m, :acc, 1)

I would say list does partial match too…

[a, b, c | rest] = [1, 2, 3, 4] # match!

You can’t do that with pattern matching. You have to write the one line function that uses if and Map.get to determine and then call x or y function.