> some kind of bucket-optimisation (multiple elements per allocation, instead of one element per allocation) should also meet all constraints the standard sets

> some kind of bucket-optimisation (multiple elements per allocation, instead of one element per allocation) should also meet all constraints the standard sets for this type Pretty sure that makes it impossible to implement merge without pointer/iterator invalidation, which is a constraint imposed by the standard (https://en.cppreference.com/w/cpp/container/unordered_map/merge https://en.cppreference.com/w/cpp/container/unordered_map/me...). > it would be good if the person I originally responded to came out and defended his POV See https://probablydance.com/2017/02/26/i-wrote-the-fastest-hashtable/ https://probablydance.com/2017/02/26/i-wrote-the-fastest-has... if you want numbers, or for example this talk by the same author https://www.youtube.com/watch?v=M2fKMP47slQ https://www.youtube.com/watch?v=M2fKMP47slQ.