#![allow(dead_code, deprecated, unused_variables, unused_mut)]
use std::io::{Write, Result};
fn main() -> Result<()> {
    let mut w = Vec::new();
    writeln!(& mut w)?;
    writeln!(& mut w, "test")?;
    writeln!(& mut w, "formatted {}", "arguments")?;
    assert_eq!(& w[..], "\ntest\nformatted arguments\n".as_bytes());
    Ok(())
}