I do whatever the elixir formatter does.

Private types are to my knowledge, only really useful within opaque types. I don’t generally use them because most of my custom types are usually named versions of the basic types. When I define structs, I type them publicly because I think of that as public API. If I were unsure of how I wanted to structure a struct, I might choose to make it opaque in that situation, so that users would only use the module I provide to interact with it. In that case the structure of the struct would be encapsulated in the module’s functions. If I used types only in the definition of the struct, I’d make those private.

I’d say most of the time it’s pretty obvious what the type is from just the name or it’s underlying type. For example, I wouldn’t need an explanation for:

@type name :: String.t()
@type server :: pid()

That’s because that’s the way the elixir formatter formats them.

When someone suggested adding something related to typespecs to credo, I seem to remember rrrene mentioning he hadn’t looked much into typespecs yet. So, it’s not a big surprise. I also completely ignored them when I first started Elixir.

I think that’s a good example where the type is opaque, so you need to know how you can create one.