#![allow(dead_code, deprecated, unused_variables, unused_mut)]
use std::fmt::Write as _;
use std::io::Write as _;
fn main() -> Result<(), Box<dyn std::error::Error>> {
    let mut s = String::new();
    let mut v = Vec::new();
    write!(& mut s, "{} {}", "abc", 123)?;
    write!(& mut v, "s = {:?}", s)?;
    assert_eq!(v, b"s = \"abc 123\"");
    Ok(())
}