Heterogeneous data with `dyn trait`

// Copyright 2025 Google LLC
// SPDX-License-Identifier: Apache-2.0

use std::fmt::Display;

pub struct Lambda;

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

fn main() {
    let heterogeneous: Vec<Box<dyn Display>> = vec![
        Box::new(42u32),
        Box::new(String::from("Woah")),
        Box::new(Lambda),
    ];
    for item in heterogeneous {
        // 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.

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Heterogeneous data with dyn trait

Heterogeneous data with `dyn trait`