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The Ultimate Guide to Rust Programming

Parameterized Fruit

Explore how to write trait implementations for parameterized structs in Rust. Understand the challenges of generic types and learn to apply trait bounds to ensure methods work across different type parameters. This lesson clarifies managing shared behavior using traits with generics.

We'll cover the following...

I said we were allowed to write a trait implementation for types we created ourselves. Let’s write a Fruit struct and provide it a Double implementation:

Rust 1.40.0
trait Double {
    fn double(&self) -> Self;
}
impl Double for i32 {
    fn double(&self) -> Self {
        self * 2
    }
}
struct Fruit {
    apples: i32,
    bananas: i32,
}
impl Double for Fruit {
    fn double(&self) -> Self {
        Fruit {
            apples: self.apples.double(),
            bananas: self.bananas.double(),
        }
    }
}
fn main() {
    let fruit = Fruit {
        apples: 5,
        bananas: 10,
    };
    println!("Apples plus bananas is {} and then doubled, apples plus bananas is {}.", fruit.apples + fruit.bananas, fruit.apples.double() + fruit.bananas.double());
}

Look at that, we were even able to reuse our double trait method inside the implementation of double for Fruit. How convenient! But after we learned about parameterized structs, it feels a bit limiting to tie ourselves down to an i32. Can we parameterize Fruit? Let’s try it. ...