trait_static_methods.rs

// Example of static methods in Rust traits, to illustrate this tweet:
// https://twitter.com/bluxte/status/1316315285356531712
//
// Try it in the Rust playground at
// https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=524057bcc33ea47ddefad9f0b31146e3

/// Something that has a name and can say it
trait NamedThing {
    /// Static method
    fn new(name: String) -> Self;
    /// Object method
    fn say_my_name(&self);
}

/// A soft spoken person
struct Whisperer {
    name: String
}

impl NamedThing for Whisperer {
    fn new(name: String) -> Self {
        // Same as `return Whisperer{name};`
        Whisperer{name}
    }

    fn say_my_name(&self) {
        println!("My name is {}", self.name.to_lowercase())
    }
}

/// A loud person
struct Yeller {
    name: String
}

impl NamedThing for Yeller {
    fn new(name: String) -> Self {
        Yeller{name}
    }

    fn say_my_name(&self) {
        println!("MY NAME IS {}", self.name.to_uppercase())
    }
}

/// From a NamedThing type and a name, create a thing and say its name
fn create_and_say_name<T: NamedThing> (name: String) -> T {
    // Constructor function to call depends on the type
    let thing = T::new(name);
    thing.say_my_name();
    thing
}

fn main() {
    // Type is inferred from the variable type
    let _whisperer: Whisperer = create_and_say_name("Joe".into());
    
    // We can also explicitely provide generic parameters
    let _yeller = create_and_say_name::<Yeller>("Jack".into());
}

// Output:
// My name is joe
// MY NAME IS JACK