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simplify the TaggedLen / set_len / capacity ... model #451
Description
the current length/capacity model is becoming hard to maintain and understand leading to strange miri provenance bugs #406
what we need conceptually is:
TaggedLen: Copy -> [onheap:1][length:63]
- default() -> Self
- new(bool, usize) -> Self
- length(self) -> usize
- onheap(self) -> bool
- get(self) -> (bool, usize)
- resize(&mut self, usize) -> ()
- relocate(&mut self, bool) -> ()
- update(&mut self, bool, usize) -> ()
and no additional methods like set_len on SmallVec
currently set_len depends on capacity its downstream methods, so this is not a simple refactor
the sketch above is just a concept
Activity
TaggedLento storeon_heapon MSB #569addandsubtoTaggedLen#570fereidani commentedon Sep 3, 2026
set_lenis a unsafe public API and which enables users to implement their own specialized optimized code, are we sure we are going to remove it?alejandro-vaz commentedon Sep 3, 2026
not removing it fully since it is on vec, but certainly not using it everywhere internally and instead operate with
self.len