CODEWITHSUNDEEP
rust
Max
Max

Reputation: 15975

Box not automatically converted to reference

I am storing a Box in a HashMap. I would like to retrieve those values and convert them into references to the boxed type. My code looks like this:

use std::collections::HashMap;

trait A {}

trait B {
    fn get(&self, key: &'static str) -> Option<&A>;
}

struct C {
    map: HashMap<&'static str, Box<A>>,
}

impl B for C {
    fn get(&self, key: &'static str) -> Option<&A> {
        return self.map.get(key)
    }
}

The error I get is: 

expected trait A, found struct `std::boxed::Box`

What is the proper way to convert Option<&Box<&A>> to Option<&A>?

Upvotes: 4

Views: 791

Answers (1)

antoyo
antoyo

Reputation: 11933

You can dereference the box and create a reference to it:

impl B for C {
    fn get(&self, key: &'static str) -> Option<&A> {
        return self.map.get(key).map(|value| &**value)
    }
}

Upvotes: 3

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