Issue #16990 has been updated by mame (Yusuke Endoh). I expect that `ary + set` return a Set, not an Array, unless it raises an exception. > Otherwise array += set would turn the variable array to a Set and that would be a surprise. It is a surprise if `ary + set` returns a collection object that is ordered and that has multiple instances in its elements. To me. `ary += set` looks like `int_val += float`. It is not a surprise to me that it changes the type of `int_val`. ---------------------------------------- Feature #16990: Sets: operators compatibility with Array https://bugs.ruby-lang.org/issues/16990#change-87438 * Author: marcandre (Marc-Andre Lafortune) * Status: Open * Priority: Normal ---------------------------------------- We currently have `set <operator> 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: <mailto:ruby-core-request / ruby-lang.org?subject=unsubscribe> <http://lists.ruby-lang.org/cgi-bin/mailman/options/ruby-core>