b+tree: move and shift a node's whole entry, not just its key - #156
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Every site that relocates values inside or between nodes named the key array directly - move_keys, rshift_keys/lshift_keys, and nine raw std::shift_left/ right calls on node.keys. That is the same thing as assuming an entry IS a key, which holds only for a set. The three helpers now carry whatever arrays make up an entry, keyed off the node type: a map's leaf has a parallel array of mapped values that has to move by the same indices, in the same direction, at the same time. Child slots are deliberately not part of an entry - relocating those has to re-index and dirty every child touched, which is what move_chldrn is for. No behavioural change: with no node carrying values yet, every added branch is constant-false and compiles away.
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Every site that relocates values inside or between nodes named the key array directly —
move_keys,rshift_keys/lshift_keys, and nine rawstd::shift_left/shift_rightcalls onnode.keys. That is the same thing as assuming an entry is a key, which holds only for a set.The three helpers now carry whatever arrays make up an entry, keyed off the node type: a map's leaf has a parallel array of mapped values that has to move by the same indices, in the same direction, at the same time. Child slots are deliberately not part of an entry — relocating those has to re-index and dirty every child touched, which is what
move_chldrnis for.No behavioural change: with no node carrying values yet, every added branch is constant-false and compiles away.
Stacked on #155.