Safely remove return statement?

1

Context: scryer-prolog/iterators.rs at l0_final · mthom/scryer-prolog · GitHub

impl<'a> Iterator for BreadthFirstIterator<'a> {
    type Item = &'a Term;

    fn next(&mut self) -> Option<Self::Item> {
        if let Some(term) = self.state_queue.pop_front() {            
            if let &Term::Clause(_, _, ref child_terms) = term {
                for term in child_terms {
                    self.state_queue.push_back(term);
                }

                return Some(term); // <-- THIS LINE
            }

            return Some(term);
        }

        None
    }
}

Can THIS LINE be safely removed ? Intuitively, I think yes, but I am trying to figure out if there is some Rust / Prolog / WAM black magic that is throwing me off.

2

Should be safe, yes. It would only be problematic if in the inner return, the variable term would be referring to something else, e. g. due to shadowing.

1 Like
3

But it is not happening right?

        if let Some(term) = self.state_queue.pop_front() {            
            if let &Term::Clause(_, _, ref child_terms) = term {
                for term in child_terms { // LINE A
                    self.state_queue.push_back(term);
                } // LINE B

                return Some(term); // <-- THIS LINE
            }

            return Some(term);
        }

The only other place where term is redefined is Line A, but that goes out of scope at Line B.

4

Yes, correct.

1 Like
5

One could go further with the rewriting and do something like

let next_term = .... pop_front();
if let Some(Term::Clause(_, _, child_terms)) = &next_term {
   for term in ....
}
next_term
2 Likes
6

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