Timely post for me as I just spent a while annotating a bunch of functions with typespecs. I’m not sure it’s my preference overall but I like the separate vs inline specs in Elixir because of function overloading and pattern matching on function defs. So if you have a function that takes an integer and does some computation based on the value of that integer you don’t need to repeat the spec for each def.

@spec foo(integer()) :: String.t()
def foo(1), do: "one"
def foo(2), do: "two"
def foo(_), do: "I'm tired"

Mostly I just wish that Elixir were statically typed. Other than that, I’d probably prefer inline type annotations as opposed to separate function specifications.

The specification keywords seem mostly fine and unsurprising even if slightly more verbose than in some other languages.

Admittedly, String.t() is the one thing that seems a little awkward, but there is a reason it ended up that way and, as you might imagine, you’ll likely forget it bothers you at some point.

If I am not mistaken typespecs were a later addition to Erlang and the idea way to not to have to change the language syntax, that is way it all resides in a module attribute.

If you use the type string() (which means a charlist) you will get a warning, you can use binary() instead (@baldwindavid shared a link about this). But String.t() means it is UTF-8.