Get name of concrete type in trait

Question

I'm implementing the Debug trait on a trait. I'd like to be able to display the name of the concrete type that implements this particular instance of the trait.

trait Node {
    foo: String,
}
    
impl fmt::Debug for dyn Node {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        let name = // get type name of self here
        write!(f, "The name: {}", name);
    }
}

I've read a number of posts about Any and downcasting and whatnot, but these solutions seem complex.

One possible solution is to add a method to the trait itself: get_name() -> String, and implement it for each struct individually. There has to be a simpler way, though.

Answer 1

We could add a get_name method to Node which returns whatever the name of Self is using std::any::type_name::<Self>().

trait Node {
    fn get_name(&self) -> &'static str {
        return std::any::type_name::<Self>();
    }
}

Inside the Debug implementation we can call self.get_name().

impl fmt::Debug for dyn Node {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        let name = self.get_name();
        write!(f, "The name: {}", name)
    }
}

Printing a dyn Node instance will show the following result:

struct SomeStruct {}
impl Node for SomeStruct {} 

fn main() {
    let a: Box<dyn Node> = Box::new(SomeStruct {});

    println!("{:?}", a)
    // The name: playground::SomeStruct
}

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Playground