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// Copyright 2025 Google LLC
// SPDX-License-Identifier: Apache-2.0
use std::fmt::Write as _;

#[derive(Default)]
struct Serializer {
    output: String,
}

impl Serializer {
    fn serialize_struct_start(&mut self, name: &str) {
        let _ = writeln!(&mut self.output, "{name} {{");
    }

    fn serialize_struct_field(&mut self, key: &str, value: &str) {
        let _ = writeln!(&mut self.output, "  {key}={value};");
    }

    fn serialize_struct_end(&mut self) {
        self.output.push_str("}\n");
    }

    fn finish(self) -> String {
        self.output
    }
}

fn main() {
    let mut serializer = Serializer::default();
    serializer.serialize_struct_start("User");
    serializer.serialize_struct_field("id", "42");
    serializer.serialize_struct_field("name", "Alice");

    // serializer.serialize_struct_end(); // ← 糟糕！忘了调用

    println!("{}", serializer.finish());
}