Debug Trait in Rust

In this quick tutorial, I will show you how to use Debug trait in Rust programming language.

For the TLDR, here is how to use Debug trait in Rust:

// 👇 Use built-in debug
#[derive(Debug)]
struct Node {
    index: i32,
    data: &'static str,
}

// 👇 Bring your own debugger
use std::fmt;

struct Node {
    index: i32,
    data: &'static str,
}

impl fmt::Debug for Node {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        return write!(f, "Node{{{},{:?}}}", self.index, self.data);
    }
}

If you want to learn more, feel free to continue below.

 Rust programming language comes with traits called  Debug as specified in  fmt module. We can use this trait to display custom debug information from our struct.

The usage is very straight forward, we just derive debug implementation via #[derive(Debug)] above the struct. For example

#[derive(Debug)]
struct Node {
    index: i32,
    data: &'static str,
}

Then you can use {:?} argument type to request Debug traits from struct Node.

let n1 = Node{index: 1, data: "Node 1"};
println!("Debug: {:?}", n1);
// Debug: Node { index: 1, data: "Node 1" }

Or we can use {:#?} argument type to pretty print the debug information

println!("Pretty: {:#?}", n1);
// Pretty: Node {
//     index: 1,
//     data: "Node 1"
// }

We can also implement Debug trait ourself, for example instead of Node {index: ..., data: ...} format. Let’s use Node{index, data} format.

The implementation available below

use std::fmt;

struct Node {
    index: i32,
    data: &'static str,
}

impl fmt::Debug for Node {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        return write!(f, "Node{{{},{:?}}}", self.index, self.data);
    }
}

Then we get our custom debug information

let n1 = Node{index: 1, data: "Node 1"};
println!("Debug: {:?}", n1);
// Debug: Node{1, "Node 1"}

So nice!