How to implement Debug for dyn Trait

help
1

How do I implement std::fmt::Debug for a custom trait?

I want to be able to print Frame in my below example.

However, I get the compile error that (dyn Series + 'static)` cannot be formatted using `{:?}` because it doesn't implement `std::fmt::Debug

I am unsure how I should implement this for Series

trait Series {
    fn len(&self) -> usize;
    //....
}

#[derive(Debug)]
struct Floats {
    data: Vec<f64>,
    name: String,
}

impl Series for Floats {
    fn len(&self) -> usize {
        self.data.len()
    }
}

#[derive(Debug)]
struct Frame {
    columns: Vec<Box<dyn Series>>,
}

fn main() {
    let f = Floats{data: vec![1.,2.],name: "H1".to_string()};
    let df = Frame{
        columns: vec![Box::new(f)],
    };
    println!("{:?}", df);
}

Thanks for your help!

1 Like
2

dyn Trait is the type on its own, and, if Trait is local to your crate (not imported), you can simply implement any trait (which does not require Self: Sized, of course) directly on trait object:

use core::fmt::Debug;
impl Debug for dyn Series {
    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        write!(f, "Series{{{}}}", self.len())
    }
}

Playground

8 Likes
3

thanks for your help. I didn‘t realize I could do this on dyn Series and was attempting to implement it on Floats which didn‘t help.

4

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