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alter :: (Eq k, Hashable k) => (Maybe v -> Maybe v) -> k -> HashMap k v -> HashMap k v |
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-- TODO(m-renaud): Consider using specialized insert and delete for alter. |
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alter f k m = |
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case f (lookup k m) of |
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Nothing -> delete k m |
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Just v -> insert k v m |
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{-# INLINABLE alter #-} |
Currently this code will attempt to delete keys that aren't present in the first place. Inserts could be more efficient too, compare alterFEager:
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alterFEager :: (Functor f, Eq k, Hashable k) |
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=> (Maybe v -> f (Maybe v)) -> k -> HashMap k v -> f (HashMap k v) |
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alterFEager f !k m = (<$> f mv) $ \case |
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|
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------------------------------ |
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-- Delete the key from the map. |
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Nothing -> case lookupRes of |
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|
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-- Key did not exist in the map to begin with, no-op |
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Absent -> m |
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|
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-- Key did exist |
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Present _ collPos -> deleteKeyExists collPos h k m |
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|
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------------------------------ |
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-- Update value |
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Just v' -> case lookupRes of |
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|
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-- Key did not exist before, insert v' under a new key |
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Absent -> insertNewKey h k v' m |
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|
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-- Key existed before |
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Present v collPos -> |
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if v `ptrEq` v' |
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-- If the value is identical, no-op |
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then m |
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-- If the value changed, update the value. |
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else insertKeyExists collPos h k v' m |
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|
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where !h = hash k |
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!lookupRes = lookupRecordCollision h k m |
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!mv = case lookupRes of |
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Absent -> Nothing |
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Present v _ -> Just v |
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{-# INLINABLE alterFEager #-} |
The Strict version has the same problems.
