From: marcandre-ruby-core@... Date: 2021-01-13T03:31:20+00:00 Subject: [ruby-core:102046] [Ruby master Feature#16989] Sets: need ♥️ Issue #16989 has been updated by marcandre (Marc-Andre Lafortune). I'm sorry, I am completely confused by this discussion, I can't make sense of it. From what I read: ```ruby set = {:a, :b, :c} # or whatever notation is used set.class # => Hash ??? set[:a] # => Hash::SetDummy ??? set[:elem] = :something_else # => what does that mean? set.to_a # => [:a, :b, :c, [:elem, :something_else]] ??? set.transform_values { ... } ??? set + [1, 2, 3] # => ??? set + Set[:d, :e] # => ??? ``` Am I understanding correctly? duerst (Martin D��rst) wrote in #note-27: > Using `Hash` for sets eliminates the efficiency problem, as we know. Are you talking about using `Hash` internally, or having Hash's class and API? > Another advantage of using Hash may be that we can get to a syntax that is very close to the actual Mathematical set syntax. We would like to write `{1, 2, 3}`, which may even be possible. I don't understand how this might be related in any way to using a Hash? What meaning we decide to give to `{a, b, c}` is completely independent to what `{a: :a, b: :b}` means, or to what `%w{a, b, c}` means, or to `{|a, b| c}` for that matter. > At the least, it should be possible to move to the following: `{1 => Hash::DummyValue, 2, 3}`, i.e. if the first key has a special value, then the remaining values can be left out. We may want to choose a better name for `Hash::DummyValue`, maybe something like `Hash::SetDummy`. Are you suggesting that instead of writing `Set[1, 2, 3]` we would literally write `{1 => Hash::SetDummy, 2, 3}`? ---------------------------------------- Feature #16989: Sets: need ������ https://bugs.ruby-lang.org/issues/16989#change-89898 * Author: marcandre (Marc-Andre Lafortune) * Status: Assigned * Priority: Normal * Assignee: knu (Akinori MUSHA) ---------------------------------------- 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. -- https://bugs.ruby-lang.org/ Unsubscribe: