Rust: Can't use HashMap<T, V> with T being an enum.

[dpc]

http://is.gd/PvCLA6

use std::collections::HashMap;

#[derive(Debug)]
enum Y {
    Y1,
    Y2,
}

#[derive(Debug)]
struct X {
    items : HashMap<Y, i8>,
}

[huonw]

HashMap has bounds on its first parameter (look at the "Methods" section): K: Eq + Hash. The slightly confusing error message is because the derived Debug implementation for X is trying to use the Debug implementation for HashMap, which has these bounds:

impl<K, V, S> Debug for HashMap<K, V, S> where K: Eq + Hash + Debug, V: Debug, S: HashState

But Y doesn't satisfy the bounds, so HashMap<Y, i8> doesn't implement Debug.

That is, your enum needs to implement those two traits, which can be done with derive:

use std::collections::HashMap;

#[derive(Debug, PartialEq, Eq, Hash)]
enum Y {
    Y1,
    Y2,
}

#[derive(Debug)]
struct X {
    items : HashMap<Y, i8>,
}

fn main()
{
    println!("Hello, world!")
}

Closing, but thanks for filing nonetheless!

[arieroos]

Can we maybe include this as a question & answer on Stack Overflow. It'll be helpful for beginners who learn through Googling their problems.