Code shared from the Rust Playground

playground.rs

use std::io::{self, Write};

#[derive(Default)]
struct Alpha {
    buf: Vec<u8>,
}

impl Write for Alpha {
    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
        self.buf.extend_from_slice(buf);
        Ok(buf.len())
    }
    fn flush(&mut self) -> io::Result<()> {
        println!(
            "[FLUSH] {}",
            String::from_utf8(self.buf.drain(..).collect()).unwrap()
        );
        Ok(())
    }
}

fn main() {
    let mut writer = io::LineWriter::new(Alpha::default());
    for _ in 0..5 {
        writeln!(&mut writer, "Hello, world!").unwrap();
    }
    println!("Ok");
    writer.flush().unwrap();
}