How to force trait implementors to support references

help
1

Hi,
I'm trying to implement a detailed custom trait. I will have two implementations, maybe more. I need to be sure that I won't miss any of the functions for other types.

I know that I can have tests checking that, but I'd like to have this checked in the trait.

The std::ops::BitOr trait has just one function fn bitor(self, rhs: Self) -> Self.

Let's talk only about u8.

It looks like for working with references, we need to implement four different versions like (BitOr in std::ops - Rust):

impl BitOr<u8> for u8
impl<'_> BitOr<&'_ u8> for u8
impl<'a> BitOr<u8> for &'a u8
impl<'_, '_> BitOr<&'_ u8> for &'_ u8

If I make my own trait, I can only require that the implementors should implement the BitOr with:

trait Ugh:
    BitOr
{}

It would be great to have this kind of reference stuff in the list of traits.

My question is: how can I ensure that the implementors of my trait will implement all four versions of the different calls with references?

thanks,
Szymon

2

You can add where bounds that use Self.

trait Ugh
where
    Self: BitOr,
    for<'a> &'a Self: BitOr,
{
    ...
}
3

Thanks,

now I have this:


trait Ugh: Sized
where
    Self: BitOr<Self>,
    for<'a> &'a Self: BitOr<Self>,
    for<'a> Self: BitOr<&'a Self>,
    for<'a> &'a Self: BitOr<&'a Self>,
{
}

It works nicely. And combined with impl_op_ex! is great. However, I wanted to automate things a little bit, as I want to add some more operators.

I have tried this:


trait BitOrTrait: Sized
where
    Self: BitOr<Self>,
    for<'a> &'a Self: BitOr<Self>,
    for<'a> Self: BitOr<&'a Self>,
    for<'a> &'a Self: BitOr<&'a Self>,
{}

trait Ugh: Sized + BitOrTrait
{
}

but then I get:

157 | trait Ugh: Sized + BitOrTrait
    |                    ^^^^^^^^^^ no implementation for `&'a Self | Self`

I have also tried moving it to a macro like:

macro_rules! add_trait_ops {
    ($op:literal) => {
        Self: $op <Self>,
        for<'a> &'a Self: $op <Self>,
        for<'a> Self: $op <&'a Self>,
        for<'a> &'a Self: $op <&'a Self>
    };
}

trait Ugh: Sized
where
    add_trait_ops!(BitOr)
{
}

but then I always have errors like unexpected token right after the macro call (regardless if I place there , or ;).

Is there a way to automate it? Macro would be the best.

thanks

4

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