Skip the tag-dictionary walk in IndexName equality when tags are identical#224
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## Summary
Adds a `===` fast path to `==` and `isequal` on `IndexName` so a comparison skips the tag-dictionary walk when both names carry the same tags object. An index leg reused across tensors carries the same `IndexName`, and therefore the same tags container, so the common equal case drops from walking the tag dictionary to a single pointer check (roughly 6.5 ns to 2.7 ns for a two-tag name).
The check sits on the tags field, which is the only costly one to compare: `uuid` and `plev` stay as the cheap primary discriminators, so names with a different id or prime level short-circuit before reaching the tags at all. This is sound because the tags are `SortedDict{Symbol, Symbol}` and `Symbol` equality is reflexive, so identical tag objects always compare equal.
Codecov Report✅ All modified and coverable lines are covered by tests. Additional details and impacted files@@ Coverage Diff @@
## main #224 +/- ##
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Coverage 76.90% 76.90%
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Files 29 29
Lines 1706 1706
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Hits 1312 1312
Misses 394 394
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mtfishman
enabled auto-merge (squash)
July 20, 2026 21:35
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Summary
Adds a
===fast path to==andisequalonIndexNameso a comparison skips the tag-dictionary walk when both names carry the same tags object. An index leg reused across tensors carries the sameIndexName, and therefore the same tags container, so the common equal case drops from walking the tag dictionary to a single pointer check.The check sits on the tags field, which is the only costly one to compare:
uuidandplevstay as the cheap primary discriminators, so names with a different id or prime level short-circuit before reaching the tags at all. This is sound because the tags areSortedDict{Symbol, Symbol}andSymbolequality is reflexive, so identical tag objects always compare equal.Comparing two two-tag
IndexNames (Julia 1.12, minimum of@benchmark, zero allocations), the equal case where both names carry the same tags object drops from about 6.5 ns to 2.7 ns. The other paths are unchanged: names with a different id short-circuit on theuuidcomparison at about 3 ns, and names with different tags fall through to the full dictionary walk at about 6 ns.