[erlang-questions] Tricking dialyzer with an opaque type

[Alex S.]

he is constructing it, after parse transform takes place.
> 30 июня 2017 г., в 14:27, Tobias Lindahl <tobias.lindahl@REDACTED> написал(а):
> 
> It seems to me that the gb_sets:from_list/1 should give the correct type for your function even if the spec is not taken into account.
> 
> In that case, the value you are getting warnings for comes from somewhere else. Could it be that you are deconstructing the opaque type somewhere?
> 
> 
> 2017-06-25 18:56 GMT+02:00 Paul Guyot <pguyot@REDACTED <mailto:pguyot@REDACTED>>:
> Hello,
> 
> I do have a parse transform that replaces the body of a 0-arity function with its result, as evaluated at compile time.
> I am looking for a way to avoid an opaque violation warning from dialyzer when this function returns, say, a gb_sets:set(). The spec is properly copied into the parsed tree, but dialyzer just ignores it.
> 
> Typically, such a function would load data from a file and create a gb_sets:set() from this data.
> 
> -spec f() -> gb_sets:set(unicode:unicode_binary()).
> f() ->
>         {ok, Content} = file:read_file(?FILENAME),
>         List0 = binary:split(Content, <<"\n">>, [global]),
>         List1 = lists:filter(fun(W) -> W =/= <<>> end, List0),
>         gb_sets:from_list(List1).
> 
> With the parse_transform, dialyzer complains on usage, e.g. :
> 
> [warning] some_module.erl:123 the call gb_sets:add(<VALUE>,Var::{1..1114111,{_,_,_}}) does not have an opaque term of type gb_sets:set(_) as 2nd argument
> 
> Yet, of course, some_module.erl does not violate the opacity of gb_sets:set() itself.
> I can trick dialyzer with an expensive identity function:
> 
>         gb_sets:add(Value, binary_to_term(term_to_binary(Var)))
> 
> Any better idea?
> 
> Paul
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