Add method to tuple-based struct

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examples/struct/tuple-as-struct-method/src/main.rs

#[derive(Debug)]
struct Color(u8, u8, u8);

impl std::fmt::Display for Color {
    fn fmt(&self, format: &mut std::fmt::Formatter) -> std::fmt::Result {
        write!(format, "RGB({}, {}, {})", self.0, self.1, self.2)
    }
}

impl Color {
    fn hex(&self) -> String {
        format!("#{:X}{:X}{:X}", self.0, self.1, self.2)
    }
}

fn main() {
    let color = Color(80, 123, 241);
    println!("{}", color);
    println!("{:?}", color);

    println!("{}", color.hex());
}

RGB(80, 123, 241)
Color(80, 123, 241)
#507BF1