[ruby-core:113434] [Ruby master Feature#19236] Allow to create hashes with a specific capacity from Ruby

Issue #19236 has been updated by Dan0042 (Daniel DeLorme). ianks (Ian Ker-Seymer) wrote in #note-8: `Hash.with_capacity` is not composable. What should you do if you want a default value/proc AND a capacity? ```ruby h = Hash.with_capacity(100) h.default = default_value #this?? a bit ugly imho ``` `Hash#with_capacity` would be better, then you could do `Hash.new(default_value).with_capacity(400)` similar to `compare_by_identity` usage. But at that point it's imho better to have `Hash.new(default_value).tap{ _1.capacity = 400 }` Or the best: `Hash.new(default_value).tap{ .capacity = 400 }` ;-) ---------------------------------------- Feature #19236: Allow to create hashes with a specific capacity from Ruby https://bugs.ruby-lang.org/issues/19236#change-103007 * 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/