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:

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

Rust

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

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

Rust

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

Rust

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

Rust

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

Rust

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

So nice!

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