Default Implementations

use std::fmt;

trait Printable: fmt::Debug + fmt::Display {
    fn print(&self) { println!("{}", self); }
    fn debug_print(&self) { println!("{:?}", self); }
    fn print_labeled(&self, label: &str) {
        println!("{}: {}", label, self);
    }
}

#[derive(Debug)]
struct Temperature(f64);

impl fmt::Display for Temperature {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "{:.1}°C", self.0)
    }
}

impl Printable for Temperature {} // All methods use defaults!

// Extending traits
trait Animal: fmt::Display {
    fn name(&self) -> &str;
    fn sound(&self) -> &str;
    fn describe(&self) -> String {
        format!("{} says '{}'", self.name(), self.sound())
    }
    fn num_legs(&self) -> u8 { 4 } // default
}

struct Dog { name: String }
impl fmt::Display for Dog {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { write!(f, "Dog({})", self.name) }
}
impl Animal for Dog {
    fn name(&self) -> &str { &self.name }
    fn sound(&self) -> &str { "woof" }
    // num_legs uses default: 4
}

struct Spider { name: String }
impl fmt::Display for Spider {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { write!(f, "Spider({})", self.name) }
}
impl Animal for Spider {
    fn name(&self) -> &str { &self.name }
    fn sound(&self) -> &str { "..." }
    fn num_legs(&self) -> u8 { 8 } // Override default
}

fn main() {
    let t = Temperature(25.0);
    t.print();
    t.print_labeled("Temp");

    let d = Dog { name: "Rex".to_string() };
    let s = Spider { name: "Charlotte".to_string() };
    println!("{} legs: {}", d.describe(), d.num_legs());
    println!("{} legs: {}", s.describe(), s.num_legs());
}