In ClickHouse, we name it ClearableHashMap: https://github.com/ClickHouse/ClickHouse/blob/master/src/Common/HashTable/ClearableHashSet.h https://github.com/Clic

In ClickHouse, we name it ClearableHashMap: https://github.com/ClickHouse/ClickHouse/blob/master/src/Common/HashTable/ClearableHashSet.h https://github.com/ClickHouse/ClickHouse/blob/master/src/Com... My colleague Michael Kolupaev, who is an ACM ICPC winner, taught me about this technique like it is some sort of common knowledge. Since then, I've been talking about it to everyone :)