How to convert BorrowTerm to String

[nwagner84]

I would like to process triples and convert the subjects, predicates and objects to strings (IRIs should be converted without angle brackets). I already got the IRI-string, but I don't know how to get the string in the else-branch. In one of my early attempts this code already worked; is there a trait or type constraint missing? Or is there a better solution?

type Input = BufReader<Box<dyn Read>>;

fn process<P>(&self, input: Input, parser: P)
where
    P: TripleParser<Input>,
{
    let mut ts = parser.parse(input);
    let _ = ts.for_each_triple(|t| {
        let s = t.s();
        let subject: Option<String> = if s.is_iri() {
            s.iri().as_deref().map(ToString::to_string)
        } else {
            Some(s.to_string())
        };

        eprintln!("subject = {:?}", subject);
    });
}

The code use sophia version 0.8.0-alpha.3.

[pchampin]

In order to make this work as is, you would need a pretty complicated type bound, but that would not really help, because not many Term implementations implement Display (which is the condition for to_string to work).

Instead, I suggest the following, where to_string is replaced with an ad-hoc function, leveraging the N-Triples serializer for all terms but IRIs.

type Input = BufReader<Box<dyn Read>>;

fn process<P>(input: Input, parser: P)
where
    P: TripleParser<Input>,
{
    let mut ts = parser.parse(input);
    let mut buf: Vec<u8> = vec![];

    let _ = ts.for_each_triple(|t| {
        let s = t.s();
        let subject: Option<String> = if s.is_iri() {
            s.iri().as_deref().map(ToString::to_string)
        } else {
            Some(stringify(s))
        };

        eprintln!("subject = {:?}", subject);
    });
}

fn stringify<T: Term>(t: T) -> String {
    let mut buf = vec![];
    sophia::turtle::serializer::nt::write_term(buf, t);
    unsafe { // safe because nt::write_term always produces valid UTF-8
        String::from_utf8_unchecked(buf)
    }
}

[nwagner84]

Many thanks!