Untagged unions (tracking issue for RFC 1444) · Issue #32836 · rust-lang/rust (original) (raw)

Tracking issue for rust-lang/rfcs#1444.

Unresolved questions:

• Does assigning directly to a union field trigger a drop of the previous contents?
• When moving out of one field of a union, are the others considered invalidated? (1, 2, 3, 4)
  • Answered by Union initialization and Drop rfcs#2514.
• Under what conditions can you implement Copy for a union? For example, what if some variants are of non-Copy type? All variants?
• What interaction is there between unions and enum layout optimizations? (Unions interacting with Enum layout optimization #36394)

Open issues of high import:

• Matching on uninhabited unsafe places (union fields, raw pointer dereferences, etc.) allowed in safe code. #47412 -- MIR-based unsafety checker sometimes accepts unsafe accesses to union fields in presence of uninhabited fields