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Implementing Traits

// Copyright 2024 Google LLC
// SPDX-License-Identifier: Apache-2.0

trait Pet {
    fn talk(&self) -> String;

    fn greet(&self) {
        println!("Oh you're a cutie! What's your name? {}", self.talk());
    }
}

struct Dog {
    name: String,
    age: i8,
}

impl Pet for Dog {
    fn talk(&self) -> String {
        format!("Woof, my name is {}!", self.name)
    }
}

fn main() {
    let fido = Dog { name: String::from("Fido"), age: 5 };
    dbg!(fido.talk());
    fido.greet();
}

  • To implement Trait for Type, you use an impl Trait for Type { .. } block.

  • Unlike Go interfaces, just having matching methods is not enough: a Cat type with a talk() method would not automatically satisfy Pet unless it is in an impl Pet block.

  • Traits may provide default implementations of some methods. Default implementations can rely on all the methods of the trait. In this case, greet is provided, and relies on talk.

  • Multiple impl blocks are allowed for a given type. This includes both inherent impl blocks and trait impl blocks. Likewise multiple traits can be implemented for a given type (and often types implement many traits!). impl blocks can even be spread across multiple modules/files.