Indicate exclude type when defining type spec

Questions / Help
1

I have a function, and its definition is shown below:

def my_func(%{a: %{b: _}}) do
      "output"
end

def my_func(_) do
      nil
end

when the input of myfunc is nested map with the key a.b, the output will be a string, or the output will be nil.

then I try to add type spec for it like below:

@spec my_func(%{a: %{b: any()}}) :: String.t()
@spec my_func(any()) :: nil
def my_func(%{a: %{b: _}}) do
      "output"
end

def my_func(_) do
      nil
end

But I receive overlapping_contract error after executing mix dialyzer. Now I’m wondering if there is a feature which can indicate the exclude type so I can add type spec like below:

@spec my_func(%{a: %{b: any()}}) :: String.t()
@spec my_func(not(%{a: %{b: any()}})) :: nil
def my_func(%{a: %{b: _}}) do
      "output"
end

def my_func(_) do
      nil
end

And of course if I just declare the input as any():

@spec my_func(any()) :: String.t() | nil
def my_func(%{a: %{b: _}}) do
      "output"
end

def my_func(_) do
      nil
end

I can easily pass the mix dialyzer. But I think the method make the type checking meaningless, because it doesn’t actually check anything, all the types of the input is OK.

2

There is no such feature.

Also, dialyzer does not attempt to narrow the range of a function according to the given arguments, so even if such a feature existed it would be equivalent to your last example.

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