Heterogeneous data with dyn trait

pub struct Lambda;

impl std::fmt::Display for Lambda {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(f, "λ")
    }
}

pub struct Heterogeneous {
    pub collection: Vec<Box<dyn std::fmt::Display>>,
}

fn main() {
    let heterogeneous = Heterogeneous {
        collection: vec![
            Box::new(42u32),
            Box::new("Woah".to_string()),
            Box::new(Lambda),
        ],
    };
    for item in heterogeneous.collection {
        // We know "item" implements Display, but we know nothing else!
        println!("Display output: {}", item);
    }
}

  • dyn Trait, being a dynamic dispatch tool, lets us store heterogeneous data in collections.

  • In this example, we’re storing types that all implement std::fmt::Display and printing all items in that collection to screen.