Traits and Generics

Traits and generics are Rust's tools for abstraction and code reuse. Traits define shared behaviour (similar to interfaces), and generics allow you to write code that works with multiple types.

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Defining Traits

A trait defines a set of methods that a type must implement:

trait Summary {
    fn summarise(&self) -> String;
}

Implementing Traits

struct NewsArticle {
    title: String,
    author: String,
    content: String,
}

impl Summary for NewsArticle {
    fn summarise(&self) -> String {
        format!("{}, by {} — {}", self.title, self.author, &self.content[..50])
    }
}

struct Tweet {
    username: String,
    content: String,
}

impl Summary for Tweet {
    fn summarise(&self) -> String {
        format!("{}: {}", self.username, self.content)
    }
}

Default Implementations

Traits can provide default method bodies:

trait Summary {
    fn summarise_author(&self) -> String;

    fn summarise(&self) -> String {
        format!("(Read more from {}...)", self.summarise_author())
    }
}

Types can override the default or use it as-is.

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Traits as Parameters

impl Trait Syntax

Accept any type that implements a trait:

fn notify(item: &impl Summary) {
    println!("Breaking news: {}", item.summarise());
}

Trait Bound Syntax

The equivalent, more explicit form: