index.md

Display trait for formatting

The Rust Display trait is a built-in trait that allows developers to format a value as a string for display purposes. It provides a human-readable representation of a type.

When a type implements the Display trait, it can be formatted as a string using the format! macro or the println! macro with the {} format specifier.

To implement the Display trait for a custom type, we define a fmt method on the type that takes a formatter object. The formatter object implements the fmt::Write trait, which provides methods for writing to a string buffer.

Example:

use std::fmt;

struct Point {
    x: i32,
    y: i32,
}

impl fmt::Display for Point {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        // The `write!` macro writes fields into the formatter
        write!(f, "x is {} and y is {}", self.x, self.y)
    }
}

fn main() {
    let p = Point { x: 1, y: 2 };
    println!("Point {}", p); // "Point x is 1 and y is 2"
}

Here, we define a fmt method for the Display trait on our Point struct. This method takes a formatter object, and writes the x field and y field of the struct into a user-friendly string.