Sophia 0.9 triples_matching return signature changes: best way to handle dynamic return types?

[KonradHoeffner]

Sorry if this is trivial to Rust experts but I ran into trouble refactoring the Sophia Graph implementation of HDT for the 0.9 changes so I just wanted to ask if there is an obvious solution to this:

The new return type signatures of triples and triples_matching now contain "impl Iterator<...>" but hdt_rs returns different types of Iterators depending on the pattern for triples_matching, so I have to use Box as shown below.
However the compiler now gives me warning: impl trait in impl method signature does not match trait method signature and advises me to add #[allow(refining_impl_trait)] to silence this warning.
However I'm hesitant to do that as I'm not sure if that has some negative consequences for the users. Shall I just silence the compiler or is there some other solution to this?

 fn triples_matching<'s, S, P, O>(&'s self, sm: S, pm: P, om: O) -> Box<dyn Iterator<Item=Result<Self::Triple<'s>, Self::Error>>  + 's>  
    where
        S: TermMatcher + 's,
        P: TermMatcher + 's,
        O: TermMatcher + 's,
    {
        let xso = match self.unpack_matcher(&sm, &IdKind::Subject) {
            None => return Box::new(iter::empty()),
            Some(x) => x,
        };
        [...]
        match (xso, xpo, xoo) {
            (Constant(s), Constant(p), Constant(o)) => Box::new(iter::once(Ok([s.0, p.0, o.0]))),
            (Constant(s), Constant(p), Other) => Box::new(
                SubjectIter::with_pattern(&self.hdt.triples, &TripleId::new(s.1, p.1, 0))
       [...]