It's not common, but it is supported
lib/elixir/lib/file.ex
1006: @spec open(Path.t, [mode | :ram]) :: {:ok, io_device} | {:error, posix}
1007: @spec open(Path.t, (io_device -> res)) :: {:ok, res} | {:error, posix}
when res: var
lib/elixir/lib/file.ex
1061: @spec open!(Path.t, [mode | :ram]) :: io_device | no_return
1062: @spec open!(Path.t, (io_device -> res)) :: res | no_return when res: var
Adding that to the Typespecs page would be good!
On Sun, 11 Dec 2016 21:56:17 +0100
Michał Muskała <[email protected]> wrote:
> As far as I know it should "just work™".
>
> Michał.
>
> > On 11 Dec 2016, at 21:11, Myron Marston <[email protected]> wrote:
> >
> > Today I was reading through http://learnyousomeerlang.com/dialyzer and
> > stumbled across this:
> >
> > -spec convert(tuple()) -> list()
> > ;
> >
> > (list()) -> tuple()
> > .
> >
> > convert(Tup) when is_tuple(Tup) -> tuple_to_list(Tup
> > );
> >
> > convert(L = [_|_]) -> list_to_tuple(L
> > ).
> >
> > Rather than putting tuple() and list() types together into a single union,
> > this syntax allows
> > you to declare type signatures with alternative clauses. If you call
> > convert/1 with a tuple, we
> > expect a list, and the opposite in the other case.
> >
> > I’ve never seen this in Elixir typespecs before and the docs make no
> > mention of Elixir
> > supporting multiple clauses in a type spec. Is this something Elixir
> > supports (or could it in
> > the future)? I can imagine a syntax like:
> >
> > @spec convert(tuple) ::
> > list
> >
> > @spec convert(list) ::
> > tuple
> >
> > def convert(tup) when is_tuple(tup), do: Tuple.to_list(tup)
> > def convert([_ | _] = list), do: List.to_tuple(list)
> > Basically, just allowing us to list multiple type spec clauses sequentially
> > like we do with
> > function clauses, with line breaks in between.
> >
> > If this is already supported, I can work on updating the type spec docs to
> > mention it.
> >
> > Thanks,
> > Myron
> >
> >
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