How to Use the Display Trait for Custom Formatting

Type System

2026-04-17T14:12:14+00:00

Implement the Display trait by defining a fmt method to control how your custom types appear in user-facing output.

Implement the Display trait for your type by defining a fmt method that takes a &self and a &mut Formatter, then use the {} placeholder in format strings to trigger custom formatting.

use std::fmt;

struct Pair<T> {
    x: T,
    y: T,
}

impl<T: fmt::Display> fmt::Display for Pair<T> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "({}, {})", self.x, self.y)
    }
}

fn main() {
    let p = Pair { x: 1, y: 2 };
    println!("Custom format: {}", p);
}