Restate Immutable's guarantees
#1165
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joshlf
requested changes
May 2, 2024
This PR adjust's `Immutable`'s informal public contract. Previously, we publicly documented that `Immutable` denoted that a type does not directly contain `UnsafeCell`. Now, we only document that `Immutable` types do not permit interrior mutation. This change is made in recognition that: - Containing `UnsafeCell` may be fine, so long as that the special properties of that `UnsafeCell` cannot be exercised in safe code. - In contrast to what's guaranteed by the compiler's `Freeze` trait, we almost certainly need *recursive* immutability for safe transmutation. Makes progress towards #1155.
joshlf
approved these changes
May 2, 2024
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This PR adjust's
Immutable's informal public contract. Previously, we publicly documented thatImmutabledenoted that a type does not directly containUnsafeCell. Now, we only document thatImmutabletypes do not permit interrior mutation.This change is made in recognition that:
UnsafeCellmay be fine, so long as that the special properties of thatUnsafeCellcannot be exercised in safe code.Freezetrait, we almost certainly need recursive immutability for safe transmutation.Makes progress towards #1155.