Issue #19236 has been updated by ianks (Ian Ker-Seymer). I worry that new Rubyists might be confused with the `Hash.new(capacity: n)` semantics. For example, `Hash[capacity: 5]` can look very similar to `Hash.new(capacity: 5)`. It wouldn’t be unreasonable to assume they are the same thing… But you’d be in for an unexpected surprise. To me `Hash.with_capacity` clearly communicates what’s happening. Anyone can understand it at first glance. ---------------------------------------- Feature #19236: Allow to create hashes with a specific capacity from Ruby https://bugs.ruby-lang.org/issues/19236#change-102984 * Author: byroot (Jean Boussier) * Status: Open * Priority: Normal * Target version: 3.3 ---------------------------------------- Followup on [Feature #18683] which added a C-API for this purpose. Various protocol parsers such as Redis `RESP3` or `msgpack`, have to create hashes, and they know the size in advance. For efficiency, it would be preferable if they could directly allocate a Hash of the necessary size, so that large hashes wouldn't cause many re-alloccations and re-hash. `String` and `Array` both already offer similar APIs: ```ruby String.new(capacity: XXX) Array.new(XX) / rb_ary_new_capa(long) ``` However there's no such public API for Hashes in Ruby land. ### Proposal I think `Hash` should have a way to create a new hash with a `capacity` parameter. The logical signature of `Hash.new(capacity: 1000)` was deemed too incompatible in [Feature #18683]. @Eregon proposed to add `Hash.create(capacity: 1000)`. -- https://bugs.ruby-lang.org/