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// Copyright 2025 Google LLC
// SPDX-License-Identifier: Apache-2.0
struct File(Option<Handle>);

impl File {
    fn open(path: &'static str) -> std::io::Result<Self> {
        Ok(Self(Some(Handle { path })))
    }

    fn write(&mut self, data: &str) -> std::io::Result<()> {
        // 必须先通过 `Option` 取得 `Handle`
        // 然后才能使用它。
        let handle = self.0.as_ref().unwrap();
        println!("write '{data}' to file '{}'", handle.path);
        Ok(())
    }
}

impl Drop for File {
    fn drop(&mut self) {
        let handle = self.0.take().unwrap();
        handle.close();
    }
}

struct Handle {
    path: &'static str,
}

impl Handle {
    fn close(self) {
        println!("Closing {}", self.path);
    }
}

fn main() -> std::io::Result<()> {
    let mut file = File::open("foo.txt")?;
    file.write("hello")?;
    Ok(())
}