A trait to require ops on references

[vandenheuvel]

I noticed e.g. this implementation to implement numerical operations on references, in this case impl<'a, 'b> Add<&'b BigInt> for &'a BigInt. Is there a trait that allows one to require that such implementations on references exist? E.g. something like below:

trait OpsOnBothValueAndRefs: NumOps<Self> + for<'r, 's> &'r Self: NumOps<'s Self> {}

[cuviper]

There are a few supertraits you can choose in various combinations of NumOps:

• Num is NumOps and a few other traits, plus a from_str_radix method.
• NumRef is Num + for<'r> NumOps<&'r Self>, basically adding a reference RHS.
• RefNum<Base> is trait that would be implemented for &Base, requiring NumOps<Base, Base> + for<'r> NumOps<&'r Base, Base> -- i.e. reference LHS, reference or value RHS.

So you could write the full combination something like this:

trait OpsOnBothValueAndRefs: NumRef
where
    for<'r> &'r Self: RefNum<Self>,
{}

However, https://github.com/rust-lang/rust/issues/20671 is the reason such a trait isn't already provided. Since the extra where clause isn't elaborated, everywhere you write T: OpsOnBothValueAndRefs, you would also have to repeat the for<'r> &'r T: RefNum<T>, which loses a lot of the value of a combined trait in the first place.

[vandenheuvel]

That explains a lot. Thank you very much!