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`impl<T: AsRawFd> AsRawFd for {Arc,Box}<T>` by jyn514 · Pull Request...

 2 years ago
source link: https://github.com/rust-lang/rust/pull/97437
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@jyn514 jyn514 commented on May 26 •

edited

This allows implementing traits that require a raw FD on Arc and Box.

Previously, you'd have to add the function to the trait itself:

trait MyTrait {
    fn as_raw_fd(&self) -> RawFd;
}

impl<T: MyTrait> MyTrait for Arc<T> {
    fn as_raw_fd(&self) -> RawFd {
        (**self).as_raw_fd()
    }
}

In particular, this leads to lots of "multiple applicable items in scope" errors because you have to disambiguate MyTrait::as_raw_fd from AsRawFd::as_raw_fd at each call site. In generic contexts, when passing the type to a function that takes impl AsRawFd it's also sometimes required to use T: MyTrait + AsRawFd, which wouldn't be necessary if I could write MyTrait: AsRawFd.

After this PR, the code can be simpler:

trait MyTrait: AsRawFd {}

impl<T: MyTrait> MyTrait for Arc<T> {}
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