Module visit

Value inspection.

The Visit trait provides a simple visitor API that can be used to inspect the structure of primitives stored in a ValueBag. More complex datatypes can then be handled using std::fmt, sval, or serde.

use value_bag::{ValueBag, Error, visit::Visit};

// Implement some simple custom serialization
struct MyVisit(Vec<u8>);
impl<'v> Visit<'v> for MyVisit {
    fn visit_any(&mut self, v: ValueBag) -> Result<(), Error> {
        // Fallback to `Debug` if we didn't visit the value specially
        write!(&mut self.0, "{:?}", v).map_err(|_| Error::msg("failed to write value"))
    }

    fn visit_u64(&mut self, v: u64) -> Result<(), Error> {
        self.0.extend_from_slice(itoa_fmt(v).as_slice());
        Ok(())
    }

    fn visit_i64(&mut self, v: i64) -> Result<(), Error> {
        self.0.extend_from_slice(itoa_fmt(v).as_slice());
        Ok(())
    }

    fn visit_f64(&mut self, v: f64) -> Result<(), Error> {
        self.0.extend_from_slice(ryu_fmt(v).as_slice());
        Ok(())
    }

    fn visit_str(&mut self, v: &str) -> Result<(), Error> {
        self.0.push(b'\"');
        self.0.extend_from_slice(escape(v.as_bytes()));
        self.0.push(b'\"');
        Ok(())
    }

    fn visit_bool(&mut self, v: bool) -> Result<(), Error> {
        self.0.extend_from_slice(if v { b"true" } else { b"false" });
        Ok(())
    }
}

let value = ValueBag::from(42i64);

let mut visitor = MyVisit(vec![]);
value.visit(&mut visitor)?;

Traits

• Visit
  A visitor for a ValueBag.