Conflicting implementations Error

help
1

Hi there, I am having some difficult in trying to implement a trait for a struct which has generics, but having slightly different code for the same method name. Below is an example of what I am trying to achieve

trait MyTrait {
    fn my_check(&self) -> bool;
}

trait MyOtherTrait {
    fn my_other_check(&self) -> bool;
}

struct Problem<C> {
    data: C,
}

trait SetData {
    fn set_data(&mut self);
}

impl<C: MyTrait> SetData for Problem<C> {
    fn set_data(&mut self) {
        // do something
    }
}

impl<C: MyTrait + MyOtherTrait> SetData for Problem<C> {
    fn set_data(&mut self) {
        // do something else
    }
}

Problem is my struct with a generic C and I want to implement the SetData trait, but do so slightly differently for when the generic C has the trait MyTrait and for when it has MyTrait and MyOtherTrait.

Any help on how to navigate around this problem would be much appreciated.

Thanks
Karl

2

This is called specialization and it's not currently possible: if you think about it, the second impl includes the first one, so which one should apply to a type that satisfies both?

You will have to re-define the problem. What is the higher-level problem you are trying to solve? There might be a completely different, easier solution.

3

Thanks for the response.

It makes sense about what you said about which one should apply; I wasnt sure if internally it would only invoke the one with two traits if they were both present.

I have some other code that will take the struct problem and call the method set_data, but i just want the method to be slightly different for the trait different traits

4

In this case, you could implement the trait for all types, and make the setter method a no-op on types which currently don't implement the trait.

5

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