mirror of
https://github.com/edg-l/edgarluque.com.git
synced 2024-09-19 17:14:22 +00:00
48 lines
1.4 KiB
Markdown
48 lines
1.4 KiB
Markdown
+++
|
|
title = "The Rust dbg! macro"
|
|
description = "A short article about a quite unknown but useful macro in Rust."
|
|
date = 2021-07-25
|
|
[taxonomies]
|
|
categories = ["rust"]
|
|
+++
|
|
|
|
The `dbg!` macro is a useful macro to debug, and I think a not well known one, not to be confused with debug logs using format strings, this macro is useful when you are about to put `println` calls everywhere in your code to know if it reached a path, what value a variable has, etc.
|
|
|
|
It uses the `Debug` trait implementation of the type of the given expression.
|
|
|
|
Since Rust is an expression oriented language, you can use this macro nearly everywhere:
|
|
|
|
```rust
|
|
fn factorial(n: u32) -> u32 {
|
|
if dbg!(n <= 1) {
|
|
dbg!(1)
|
|
} else {
|
|
dbg!(n * factorial(n - 1))
|
|
}
|
|
}
|
|
|
|
fn main() {
|
|
dbg!(factorial(4));
|
|
}
|
|
```
|
|
|
|
This outputs the following:
|
|
|
|
```
|
|
[src/main.rs:2] n <= 1 = false
|
|
[src/main.rs:2] n <= 1 = false
|
|
[src/main.rs:2] n <= 1 = false
|
|
[src/main.rs:2] n <= 1 = true
|
|
[src/main.rs:3] 1 = 1
|
|
[src/main.rs:5] n * factorial(n - 1) = 2
|
|
[src/main.rs:5] n * factorial(n - 1) = 6
|
|
[src/main.rs:5] n * factorial(n - 1) = 24
|
|
[src/main.rs:10] factorial(4) = 24
|
|
```
|
|
|
|
Using this macro without any argument will print the current file and line number.
|
|
|
|
One thing to be aware is that this macro moves the input, in cases where this is a problem it's useful to borrow.
|
|
|
|
Sources:
|
|
- <https://doc.rust-lang.org/std/macro.dbg.html> |