From: marcandre-ruby-core@... Date: 2020-09-03T23:29:36+00:00 Subject: [ruby-core:99905] [Ruby master Feature#16990] Sets: operators compatibility with Array Issue #16990 has been updated by marcandre (Marc-Andre Lafortune). knu (Akinori MUSHA) wrote in #note-4: > We can probably define Set#to_ary if it's OK, and Array#+ will be able to deal with a set. Let us think about the downsides... While this may be a good thing, and at least make them interoperable, it is still quite inefficient... For example, `Array#-` would call `to_ary`, which would create a temporary array from the hash, only to create a temporary hash/set... > As for the result type, I think Array operators should return arrays. Otherwise array += set would turn the variable array to a Set and that would be a surprise. Indeed. I'm glad we agree ���� ---------------------------------------- Feature #16990: Sets: operators compatibility with Array https://bugs.ruby-lang.org/issues/16990#change-87436 * Author: marcandre (Marc-Andre Lafortune) * Status: Open * Priority: Normal ---------------------------------------- We currently have `set array` work fine: ```ruby Set[1] + [2] # => Set[1, 2] ``` Nothing works in the reverse order: ```ruby [1] + Set[2] # => no implicit conversion of Set into Array # should be: [1] + Set[2] # => [1, 2] ``` #### set-like operators Note that the situation is particularly frustrating for `&`, `|` and `-`. If someone wants to do `ary - set`, one **has** to do `ary - set.to_a` which will, internally, do a `to_set`, so what is happening is `set.to_a.to_set`!! (assuming `ary` is over `SMALL_ARRAY_LEN == 16` size, otherwise it's still doing in `O(ary * set)` instead of `O(ary)`). The same holds with `&` and `|`; see order issue as to why this can *not* (officially) be done any other way. Reminder: ```ruby ary & ary.reverse # => ary Set[*ary] & Set[*ary.reverse] # => Set[*ary.reverse], officially order is indeterminate ``` -- https://bugs.ruby-lang.org/ Unsubscribe: