Rust Formatter.fill用法及代碼示例

use std::fmt;

struct Foo;

impl fmt::Display for Foo {
    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
        let c = formatter.fill();
        if let Some(width) = formatter.width() {
            for _ in 0..width {
                write!(formatter, "{}", c)?;
            }
            Ok(())
        } else {
            write!(formatter, "{}", c)
        }
    }
}

// We set alignment to the right with ">".
assert_eq!(&format!("{:G>3}", Foo), "GGG");
assert_eq!(&format!("{:t>6}", Foo), "tttttt");