Avoid intermediate Map allocations in groupFlatMap#79
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The Result/AbstractFunction1 pattern finalized builders via repeated calls to immutable.Map#updated, which rebuilds parts of the HashMap trie on every call and discards all but the final version as garbage. Replace it with view.mapValues(_.result()).toMap, which stages results in a single Map builder and freezes it once. Same O(n + k) complexity (n = elements, k = groups), fewer allocations. Enhanced the test in group-flat-map.scala to cover more cases.
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The Result/AbstractFunction1 pattern finalized builders via repeated calls to immutable.Map#updated, which rebuilds parts of the HashMap trie on every call and discards all but the final version as garbage.
Replace it with view.mapValues(_.result()).toMap, which stages results in a single Map builder and freezes it once. Same O(n + k) complexity (n = elements, k = groups), fewer allocations.
Enhanced the test in group-flat-map.scala to cover more cases.