[ruby-core:111931] [Ruby master Feature#19236] Allow to create hashes with a specific capacity from Ruby

Issue #19236 has been updated by byroot (Jean Boussier). Well, `Hash.new(capacity: 4096)` was definitely my first pick, so this is great news IMO. What would be the timeline? Deprecate in 3.3 and break in 3.4? I think it's in part because `Array.new(4096)` while not exactly the same, already somewhat works. I'd be happy to add `Array.new(capacity: 4096)` though, but it has a similar backward compatibility concern doesn't it? ---------------------------------------- Feature #19236: Allow to create hashes with a specific capacity from Ruby https://bugs.ruby-lang.org/issues/19236#change-101358 * 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/