How do I compare an Arc<T> against a T?

user_4808079 0
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I'm trying to treat Arc more like its underlying data, in particular I'm trying to use overloaded operators. The following code gives errors but was my attempt.

use std::cmp::Ordering;
use std::option::Option;
use std::sync::Arc;

pub struct SomeNum {
    num: u32,
}

impl std::cmp::PartialEq<u32> for SomeNum {
    fn eq(&self, other: &u32) -> bool {
        return *other == self.num;
    }
}

impl std::cmp::PartialOrd<u32> for SomeNum {
    fn partial_cmp(&self, other: &u32) -> Option<Ordering> {
        if (self.num < *other) {
            return Option::Some(Ordering::Less);
        }
        if (self.num > *other) {
            return Option::Some(Ordering::Greater);
        }
        return Option::Some(Ordering::Equal);
    }
}

fn main() {
    let test_num = SomeNum { num: 16 };
    let oveloadedNum = test_num > 10; // works

    let arc_num = Arc::new(test_num);
    let overloadedArc = arc_num > 10; // fails

    let arc_num_clone = Arc::clone(&arc_num);
    let overloadedArcClone = arc_num_clone > 10; // fails
}

playground

I tried using impl Arc<SomeNum> but you can't do that for things outside of your crate. Beyond this, I'm very very new to Rust (day 2), so I feel like I'm missing something obvious. Perhaps I could extend Arc, then implement stuff for it?

rust operator-overloading
1 Answers

Your Arc can be used as SomeNum because it is dereferenced whenever you call a function on it. If you have a look at the documentation of Arc, you will see that dereferencing Arc<T> results in a T.

You have implemented PartialOrd and PartialEq only for the struct SomeNum, so > will only work with SomeNum. You have to dereference your Arcs before comparing them.

fn main() {
    let test_num = SomeNum { num: 16 };
    let oveloadedNum = test_num > 10; // works

    let arc_num = Arc::new(test_num);
    let overloadedArc = *arc_num > 10;

    let arc_num_clone = Arc::clone(&arc_num);
    let overloadedArcClone = *arc_num_clone > 10;
}
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