Serializer: implement Root

#![allow(unused)]
fn main() {
use std::fmt::Write as _;
struct Serializer<S> {
    // [...]
    indent: usize,
    buffer: String,
    state: S,
}

struct Root;
struct Struct<S>(S);

impl Serializer<Root> {
    fn new() -> Self {
        // [...]
        Self { indent: 0, buffer: String::new(), state: Root }
    }

    fn serialize_struct(mut self, name: &str) -> Serializer<Struct<Root>> {
        // [...]
        writeln!(self.buffer, "{name} {{").unwrap();
        Serializer {
            indent: self.indent + 1,
            buffer: self.buffer,
            state: Struct(self.state),
        }
    }

    fn finish(self) -> String {
        // [...]
        self.buffer
    }
}
}

Referring back to our original diagram of valid transitions, we can visualize the beginning of our implementation as follows:

Serializer[Root]Serializer[Struct[Root]]Stringserializestructfinishstructfinish
  • At the “root” of our Serializer, the only construct allowed is a Struct.

  • The Serializer can only be finalized into a String from this root level.