[erlang-questions] type specification
Sat Jul 3 09:21:31 CEST 2010
Zoltan Lajos Kis wrote:
> Could you explain how the new export_type attribute relates to the
> opaque attribute?
Declaring a type as opaque means that you want to keep the structure
private to the defining module (which of course can manipulate the
structure of such terms) and prevent other modules from doing operations
to such a term that depends on its structure; dialyzer will warn you
about such uses. Because the defining module can always manipulate the
structure of such terms, it does not make sense to declare a type as
opaque in some module and have it module-local (i.e., not exported).
Thus, an opaque type should always be exported.
> In R14A it seems that if I define an opaque type (without exporting it),
> and try to use it in another module, dialyzer emits an unknown type
Yes, this is expected. You can not use remote types (types defined in
some other module) that are not exported by the defining module.
> If I export the type the warning is not emitted, but the type is not
> treated as opaque anymore...
Either I do not understand what you mean here, or I doubt this. A small
code example with the behavior you observe will help here (perhaps off
list, if it is too big).
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