paulk-asert commented on code in PR #665:
URL:
https://github.com/apache/commons-collections/pull/665#discussion_r2621377853
##########
src/main/java/org/apache/commons/collections4/MultiMapUtils.java:
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@@ -170,6 +171,27 @@ public static boolean isEmpty(final MultiValuedMap<?, ?>
map) {
return map == null || map.isEmpty();
}
+ /**
+ * A utility method to invert the mappings from a source MultiValuedMap
Review Comment:
You could write a method that worked with ordinary maps. Given that ordinary
maps don't need the value to be a collection, there are multiple possible
semantics. One potential behavior would be to throw a runtime exception if
called with a map having a value that isn't a collection. Another semantic
might coerce the value into a singleton collection. Other libraries tend to
have factory methods for creating a multimap from an ordinary map - different
factory methods could provide different semantics. Then the invert method just
works with multimaps. Commons Collections already has such factory methods,
e.g. `HashSetValuedHashMap(Map)`.
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