Cherry-pick FCollection from #11366 - #11431
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FCollection kept a HashSet beside its list purely to reject duplicate adds and answer contains() in O(1). Trait rebuilds (getReplacementEffects / getStaticAbilities / getTriggers, plus every FCollection copy they make) create tens of millions of these per game, almost all holding one or two elements and never queried by value - so the set was pure overhead: an extra allocation per collection and a hash insert per element. Build the set on demand instead. Until something needs value semantics at scale (asSet, or growth past a small threshold) uniqueness is enforced by scanning the list, which is cheaper than the set for the tiny sizes that dominate. Also copy straight across the backing list when constructing from another FCollection (the source already guarantees uniqueness) and skip iterating empty collections in addAll. Verified against a fixed 5-seed AI-vs-AI match on a 510-card deck: every game's end state is byte-identical to before, and total match time drops substantially (the set churn was the single largest allocation source in the profile). Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Hanmac
approved these changes
Jul 27, 2026
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@Hanmac
I looked into just using
LinkedHashSetbut it's missing too many methods imo.