Debug and Display trait and macros

Debug and Display trait

In Rust, the Debug and Display traits are part of the standard library, and they allow you to control how an object is printed or formatted as a string.

Debug:
- The Debug trait is used to provide a formatted representation of an object for debugging purposes.
- It’s generally used with the {:?} syntax when printing or formatting objects.
```
println("{:?}", v);
```
Display:
- The Display trait is used to provide a user-friendly string representation of an object.
- It’s used with the {} syntax when formatting or printing objects.

println("{}", v);

Deriving `Debug` / `Display` on your own struct

Lets say you have your own struct called Rect

struct Rect {
  width: u32,
  height: u32
}

fn main() {
    let s = Rect {
        width: 100,
        height: 100
    };
    println!("{}", s);
}

If you try printing a rectangle, you will see the following error

Screenshot 2025-02-21 at 5.38.47 PM.png

Implementing the `Display` trait manually

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

Implementing the `Debug` trait manually

use std::fmt;

struct Rect {
  width: u32,
  height: u32
}

impl std::fmt::Debug for Rect {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "({}, {})", self.width, self.height)
    }
}

fn main() {
    let s = Rect {
        width: 100,
        height: 100
    };
    println!("{:?}", s);
}

Deriving the `Debug` trait using the `Debug macro`

use std::fmt;

#[derive(Debug)]
struct Rect {
  width: u32,
  height: u32
}

fn main() {
    let s = Rect {
        width: 100,
        height: 100
    };
    println!("{:?}", s);
}

Difference between `Debug` and `Derive`

The difference between the Debug and Display traits in Rust is rooted in their intended purpose and the way they represent data.

Debug - Primarily intended for debugging and inspecting values in a developer-friendly format.

Display - The Display trait is intended for user-facing output, focusing on simplicity and readability. It’s used when you want to format an object in a way that’s easy to understand for end users.

Debug and Display trait and macros