Should I provide typespec for each function clause?

Questions / Help
1

When creating multiple clauses for a function, should I provide typespec for each one? Example:

@spec foo([]) :: {:error, any}
def foo([]) do
  ...
  {:error, ...}
end

@spec foo([integer]) :: {:ok, any}
def foo(some_list) do
  ...
  {:ok, ...}
end

…or is something like this preferrable?


@spec foo([integer]) :: {:ok, any} | {:error, any}

def foo([]) do
  ...
  {:error, ...}
end

def foo(some_list) do
  ...
  {:ok, ...}
end

Thanks!

2

Both work, internally there’s no difference and the multiple specs will become unions of all separate specs anyways.

3

I’ll typically use the second approach.

The different function heads which ultimately need to be defined by the spec are typically grouped together and having a spec at the top of that group makes for a reasonable signpost in the source code for the beginning of that group.

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4

You are defining ONE function so it should be for that function which you give the typespec.

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