Implement an O(1) stack treemap move iterator #10214
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Because the move iterator contains ownership of the tree, we can destructure it as we go (and modify the internal structure). This also allows us to make the move iterator for a treemap invertable and exactly sized (for an enumerable variant). Sadly, I know of no way to extend this to a normal iterator, so iter() will still require a stack allocation for now. Additionally, this implements the clear() method in terms of move_iter() to force O(1) stack usage when clearing a tree. I tried to implement this in a Drop implementation for `TreeMap` as well, but I ran into ICE problems about some missing vtables, so I'll leave that implementation for a later date. The idea would be that dropping a `TreeMap` requires O(1) stack space instead of O(depth) stack space.
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Does this work when alternating |
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Ah, I should probably add a test yes. It's incredibly inefficient (because you're rotating everything one way and then the other), but it does work. |
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Ah cool! Might be worth mentioning the inefficiency in the docs? |
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The maximum depth is |
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Hm, I didn't think too hard about this. A log2(n) depth is nothing to worry about at all. |
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…h,giraffate Changelog for Rust 1.67 🐞 Roses are red, violets are blue, if changelogs could talk, what would we do? --- The usual disclaimer: This PR is written, as if the version was already released. It should be merged with the coming release on 2023-01-26. So, please provide feedback and approve it, if everything looks good, but let's wait with the r+ until the release :) --- changelog: none
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Because the move iterator contains ownership of the tree, we can destructure it
as we go (and modify the internal structure). This also allows us to make the
move iterator for a treemap invertable and exactly sized (for an enumerable
variant). Sadly, I know of no way to extend this to a normal iterator, so iter()
will still require a stack allocation for now.
Additionally, this implements the clear() method in terms of move_iter() to
force O(1) stack usage when clearing a tree. I tried to implement this in a Drop
implementation for
TreeMapas well, but I ran into ICE problems about somemissing vtables, so I'll leave that implementation for a later date. The idea
would be that dropping a
TreeMaprequires O(1) stack space instead of O(depth)stack space.