Implement Debug trait for large array type

Question

I gather that Rust provides Debug impl's for arrays size 32 and smaller.

I also gather that I could implement Debug on a larger array by simply using write! with a very long format specifier. But I'm wondering if there's a better way.

What is the recommended method for implementing Debug for an array of length, say, 1024?

I'd say that depends entirely on your use case. I've had cases where I needed to see every last value of my data. Sometimes, it's enough to write out some statistics about the data. It's your data, after all. — llogiq
Good point. And while I wait for an answer, I'm doing just that, printing a few important bits of information. But I'm still curious if there's a good way to print the entire array. — user12341234
you don't need a very long format -- any array is printable as a slice. — bluss

A.B. A.B. · Accepted Answer · 2015-06-17T22:03:03

use std::fmt;

struct Array<T> {
    data: [T; 1024]
}

impl<T: fmt::Debug> fmt::Debug for Array<T> {
    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
        self.data[..].fmt(formatter)
    }
}

fn main() {
    let array = Array { data: [0u8; 1024] };

    println!("{:?}", array);
}

It's not possible to implement Debug for [T; 1024] or some array of a concrete type (ie. [u8; 1024]. Implementing traits from other crates for types from other crates, or implementing a trait from another crate for a generic type, are both not allowed by design,

Implement Debug trait for large array type

1 Answers