From: janosch-x via ruby-core <ruby-core@...>
Date: 2022-12-25T17:16:47+00:00
Subject: [ruby-core:111425] [Ruby master Feature#19236] Allow to create hashes with a specific capacity from Ruby

Issue #19236 has been updated by janosch-x (Janosch M�ller).





maybe the genie is out of the bottle already, but it would be nice to have a uniform API for creating objects with a given capacity, e.g.



```ruby

Array.with_capacity(100)      # => []

Hash.with_capacity(100)       # => {}

IO::Buffer.with_capacity(100) # => #<IO::Buffer>

String.with_capacity(100)     # => ''

# more?

```



for `Array` and `IO::Buffer`, `::with_capacity` would essentially be an alias for `::new`. for `String`, the `capacity` kwarg could be deprecated to limit the number of APIs.



----------------------------------------

Feature #19236: Allow to create hashes with a specific capacity from Ruby

https://bugs.ruby-lang.org/issues/19236#change-100797



* 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)`.











-- 

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