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[extension types] Member conflicts ignore precluded members #3486

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merged 2 commits into from
Dec 1, 2023
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[extension types] Member conflicts ignore precluded members #3486

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f9fbae1
Adjust rules about extension type member conflicts: precluded members…
eernstg Nov 28, 2023
c35b30c
Add mixed member case: precluded members do not create a conflict
eernstg Nov 28, 2023
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9 changes: 5 additions & 4 deletions accepted/future-releases/extension-types/feature-specification.md
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Expand Up @@ -906,8 +906,9 @@ On the other hand, it can occur in other ways, e.g., as a type argument of
a superinterface of a class.*

It is a compile-time error if _DV_ is an extension type declaration, and
_DV_ has a non-extension type member named `m` as well as an extension type
member named `m`, for any `m`. *In case of conflicts, _DV_ must declare a
_DV_ has a non-extension type member named `m` which is not precluded by
_DV_ as well as an extension type member named `m` which is not precluded
by _DV_, for any `m`. *In case of conflicts, _DV_ must declare a
member named `m` to resolve the conflict.*

It is a compile-time error if _DV_ is an extension type declaration, and
Expand All @@ -918,8 +919,8 @@ conflict.*

A compile-time error occurs if an extension type declaration _DV_ has
two extension type superinterfaces `V1` and `V2`, and both `V1` and `V2`
has an extension type member named `m`, and the two members have distinct
declarations.
has an extension type member named `m` that is not precluded by _DV_, and
the two members have distinct declarations.

*In other words, an extension type member conflict is always an error, even
in the case where they agree perfectly on the types. _DV_ must override the
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