It is called a function head. It is useful, as @brettbeatty said, for optional args and docs, but also simply to give a name to the opt variable, which is good to have in docs. (Although here it is a private function so that does not count 
)
lud
1
stevensonmt
At the risk of this thread becoming too wide ranging, when is it appropriate to define functions multiple times for different types versus defining a single function that matches a case statement on the arg? Something like:
defp put_opt(opt, acc) do
case opt do
a when is_integer(a) -> %{ acc | a: a }
b when is_binary(b) -> %{acc | b: b }
...
end
^written on the fly, not sure if that would compile but hoping it gets the idea across.
0
RudManusachi
It depends. While, IMHO, it’s easier to begin with case do, if the body of different branches of case is getting larger it’s nicer to break it into multiple functions. Plus multiple functions if fail - will give you better backtrace info on where to look at. Also, to me, it’s somewhat easier to read when the whole body of the function describes one path rather than keeping condition context in mind.
Or, just whatever is easier to read =)
1