We make 5 changes:
- Allow `require Self impls I` in an `interface` or `constraint` scope
to omit the `Self`, so it can be written `require impls I`.
- Rename `extend I` to `extend require impls I` in an `interface` or
`constraint` scope.
- Define `extend impl as I` and `extend final impl as I` in an
`interface` scope to copy the members of `I` and define an `impl` of `I`
in terms of the extending interface.
- Allow a non-final `impl` to overlap a final `impl` as long as it isn't
subsumed by the final `impl`. The final `impl` will be given priority on
the overlap.
- Allow `final` on a `match_first` block, used to declare overlapping
final impls.
These features work together to allow a form of interface extension
where:
- Types only need to `impl` the extending interface to also get an
`impl` of the extended interface.
- Multiple interfaces can extend the same interface.
- An interface can extend multiple interfaces.
---------
Co-authored-by: Josh L <josh11b@users.noreply.github.com>
Co-authored-by: Richard Smith <richard@metafoo.co.uk>
Co-authored-by: Dana Jansens <danakj@orodu.net>
Co-authored-by: Carbon Infra Bot <carbon-external-infra@google.com>
Co-authored-by: Chandler Carruth <chandlerc@gmail.com>
This directory contains accepted proposals for the carbon-lang repository. For
information about declined/deferred proposals, please view the proposal's
original pull request.
For accepted proposals, where #### is the corresponding proposal's pull
request:
p####.md will contain the main proposal text.
p#### may be present as an optional subdirectory for related files (for
example, images).
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