Yep. I LOVE this pattern and use it excessively at times in a large variety of languages. ^.^
OvermindDL1
NobbZ
Phantom types… Never used them in elixir, as I usually use types and specs for documentation only.
I rarely use dialyzer itself. Just ran it in a handfull of projects recently to test the new error-message-translator 
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OvermindDL1
Those are Named Types. Phantom types are zero-sized types added to a larger type who’s whole purpose is to carry type information (with no associated values) ‘through’ something to be used elsewhere. 
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OvermindDL1
A prime simple example in OCaml’ize is:
type EscapedString = EscapedString string
let escape_string str = EscapedString (escape_whatever str)
let to_string (EscapedString str) = str
let render (EscapedString str) = do_render str
And so forth. Essentially it just enforces you to make sure that you run something through, say, a validator before it can be used, in the above case it is to make sure the string is escaped before it is rendered for example.
EDIT: Or for things like tagging integers to keep them distinct for memory arrays for a text-adventure engine emulator so you can’t accidentally use the wrong value in the wrong memory chunk.
It’s basically Manually Made Refined Typing… ^.^;
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xvw
Yes, Phantom types uses a (ore more) “polymorphic parameter(s)” which are not used in the body of the types. Elixir/Erlang (via Dialyzer) does not support (I think) concept of “variance”, so I suppose that the usage of Phantom Types could be limited.
Btw, I did not known the name “Named Types”. Thanks @OvermindDL1
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