Comprehensive Rust 🦀

Serializer: Root を実装する

// Copyright 2025 Google LLC
// SPDX-License-Identifier: Apache-2.0

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
    }
}

元の有効な遷移の図を振り返ると、実装の冒頭は次のように視覚化できます。