Error on declaring a bitstring type

[Iuri Machado]

Hi everyone, I'm trying to do this:

@type client_login_message :: <<_::size(8),
                                _::unsigned-little-integer-size(16),
                                _::unsigned-little-integer-size(32),
                                _::size(8),
                                _::size(8),
                                _::size(8),
                                _::unsigned-little-integer-size(16),
                                _::unsigned-little-integer-size(32),
                                _::unsigned-little-integer-size(32),
                                _::unsigned-little-integer-size(32),
                                _::unsigned-little-integer-size(32),
                                _::unsigned-little-integer-size(32),
                                _::size(8),
                                _::byte>>

But I'm receiving an error while compiling:

== Compilation error on file lib/realm/messages/logon_challenge.ex ==
** (CompileError) lib/realm/messages/logon_challenge.ex:32: type '<<>>'(_) undefined
    (stdlib) lists.erl:1337: :lists.foreach/2
    (stdlib) erl_eval.erl:670: :erl_eval.do_apply/6

Any ideas?

[José Valim]

The typespec for bitstrings is limited to only the size and unit:

http://elixir-lang.org/docs/master/elixir/typespecs.html

It seems you want: <<_::8>> (or simply binary()).

José Valim

www.plataformatec.com.br

Skype: jv.ptec

Founder and Director of R&D

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[Iuri Machado]

Thanks Valim!

Just a little following, is there a reason for this limitation?

[José Valim]

I am actually not sure. The typespecs mechanism simply delegates to Erlang and Dialyzer. I suppose it is because that's the maximum amount of information that the Dialyzer can use from the bitstrings typespecs.

José Valim

www.plataformatec.com.br

Skype: jv.ptec

Founder and Director of R&D