[ruby-core:102042] [Ruby master Feature#16989] Sets: need ♥️

Issue #16989 has been updated by akr (Akira Tanaka).


akr (Akira Tanaka) wrote in #note-25:

> - Hash#each doesn't work well as Set but we can use Hash#each_key.

To be fair, "Hash#each doesn't work well" means Enumerable methods doesn't work well.
`enum_for(:each_key)` can be used as `{1, 2}.enum_for(:each_key).max`, though.

(I forgot to mention that Ruby can interpret `{1, 2}` as `{ 1 => Hash::SetDummy, 2 => Hash::SetDummy }`.  I feel the name SetDummy is better than DummyValue.  Thanks.)

It may be possible to solve this by Hash#each yields `key` instead of `[key, value]` if `value` is `Hash::SetDummy`.
I doubt it will be accepted, though.





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Feature #16989: Sets: need ♥️
https://bugs.ruby-lang.org/issues/16989#change-89894

* Author: marcandre (Marc-Andre Lafortune)
* Status: Assigned
* Priority: Normal
* Assignee: knu (Akinori MUSHA)
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I am opening a series of feature requests on `Set`, all of them based on this usecase.

The main usecase I have in mind is my recent experience with `RuboCop`. I noticed a big number of frozen arrays being used only to later call `include?` on them. This is `O(n)` instead of `O(1)`.

Trying to convert them to `Set`s causes major compatibility issues, as well as very frustrating situations and some cases that would make them much less efficient.

Because of these incompatibilities, `RuboCop` is in the process of using a custom class based on `Array` with optimized `include?` and `===`. `RuboCop` runs multiple checks on Ruby code. Those checks are called cops. `RuboCop` performance is (IMO) pretty bad and some cops  currently are in `O(n^2)` where n is the size of the code being inspected. Even given these extremely inefficient cops, optimizing the 100+ such arrays (most of which are quite small btw) gave a 5% speed boost.

RuboCop PRs for reference: https://github.com/rubocop-hq/rubocop-ast/pull/29
https://github.com/rubocop-hq/rubocop/pull/8133

My experience tells me that there are many other opportunities to use `Set`s that are missed because `Set`s are not builtin, not known enough and have no shorthand notation.

In this issue I'd like to concentrate the discussion on the following request: `Set`s should be core objects, in the same way that `Complex` were not and are now. Some of the upcoming feature requests would be easier (or only possible) to implement were `Set`s builtin.



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