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Implement Encode for unsized types as well #9

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Aug 31, 2021
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Implement Encode for unsized types as well #9

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26 changes: 15 additions & 11 deletions src/encode.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -79,25 +79,29 @@ slice_encode_impl!(
27, 28, 29, 30, 31, 32
);

/*
External crates cannot implement Encode for pointers or Optionals, but they
*can* implement it for references. rust-lang/rust#25126

As a workaround, we provide implementations for these types that return the
same encoding as references.
*/
unsafe impl<T> Encode for *const T where for<'b> &'b T: Encode {

// External crates cannot implement Encode for pointers or [`Option`], but
// they *can* implement it for references. See
// [rust-lang/rust#25126](https://github.com/rust-lang/rust/issues/25126)
//
// So, as a workaround, we provide implementations for these types that return
// the same encoding as references.
//
// Using `?Sized` is safe here because we delegate to other implementations
// (which will verify that the implementation is safe for the unsized type).

unsafe impl<T: ?Sized> Encode for *const T where for<'b> &'b T: Encode {
const ENCODING: Encoding<'static> = <&T>::ENCODING;
}

unsafe impl<T> Encode for *mut T where for<'b> &'b mut T: Encode {
unsafe impl<T: ?Sized> Encode for *mut T where for<'b> &'b mut T: Encode {
const ENCODING: Encoding<'static> = <&mut T>::ENCODING;
}

unsafe impl<'a, T> Encode for Option<&'a T> where for<'b> &'b T: Encode {
unsafe impl<'a, T: ?Sized> Encode for Option<&'a T> where for<'b> &'b T: Encode {
const ENCODING: Encoding<'static> = <&T>::ENCODING;
}

unsafe impl<'a, T> Encode for Option<&'a mut T> where for<'b> &'b mut T: Encode {
unsafe impl<'a, T: ?Sized> Encode for Option<&'a mut T> where for<'b> &'b mut T: Encode {
const ENCODING: Encoding<'static> = <&mut T>::ENCODING;
}