Pointee not on the heap? [LWN.net]

Pointee not on the heap?

Posted Apr 23, 2026 11:43 UTC (Thu) by daroc (editor, #160859)
In reply to: Pointee not on the heap? by pbonzini
Parent article: One Sized trait does not fit all

Oops — that's my mistake. Yes, you're right that C could return any kind of pointer it likes. Pointee is supposed to be completely opaque, so that should be fine.

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Pointee not on the heap?

Posted Apr 23, 2026 13:42 UTC (Thu) by pbonzini (subscriber, #60935) [Link] (1 responses)

Even if on the stack, C could pass it into a callback :)

Pointee not on the heap?

Posted Apr 23, 2026 14:19 UTC (Thu) by daroc (editor, #160859) [Link]

True! I guess the precise way of saying what's going on with Pointee is "it can't be used in any place that requires Rust code to have knowledge of its size, meaning that it can only be stored as the last element of (heap-allocated) Rust structures and must always be interacted with via a pointer of some kind, even if that is a fake 'pointer' invented by C code", but that doesn't really fit in the little summary table. So given the surrounding article for context, I'm comfortable summarizing those rules as "not on the stack". :)