[ruby-core:111781] [Ruby master Feature#19324] Enumerator.product => Enumerable#product

Issue #19324 has been updated by sawa (Tsuyoshi Sawada). zverok (Victor Shepelev) wrote in #note-4: I believe quite many people are in favor of `Array.product` and/or `Array.zip`. I wish the implementation/existence of `Enumerator.product` will work as a pressure towards implementing these methods as well. However, I do not think many other methods like those you mention would need to be handled similarly for the sake of consistency; (i) `Array#product` and `Array#zip` are different from (ii) `Hash#merge` and `Array#concat`. The (ii) methods with multiple arguments are nothing more than a repetition of binary operations (and furthermore, they are associative): ```ruby [1, 2, 3].concat([4, 5, 6], [7, 8, 9]) == [1, 2, 3].concat([4, 5, 6]).concat([7, 8, 9]) == [1, 2, 3].concat([4, 5, 6].concat([7, 8, 9])) # => [1, 2, 3, 4, 5, 6, 7, 8, 9] {a: 1}.merge({b: 2}, {c: 3}) == {a: 1}.merge({b: 2}).merge({c: 3}) == {a: 1}.merge({b: 2}.merge({c: 3})) # => {:a=>1, :b=>2, :c=>3} ``` whereas the (i) methods are not: ```ruby [1, 2].zip([3, 4], [5, 6]) # => [[1, 3, 5], [2, 4, 6]] [1, 2].zip([3, 4]).zip([5, 6]) # => [[[1, 3], 5], [[2, 4], 6]] [1, 2].zip([3, 4].zip([5, 6])) # => [[1, [3, 5]], [2, [4, 6]]] [1, 2, 3].zip([4, 5, 6], [7, 8, 9]) # => [[1, 4, 7], [2, 5, 8], [3, 6, 9]] [1, 2, 3].zip([4, 5, 6]).zip([7, 8, 9]) # => [[[1, 4], 7], [[2, 5], 8], [[3, 6], 9]] [1, 2, 3].zip([4, 5, 6].zip([7, 8, 9])) # => [[1, [4, 7]], [2, [5, 8]], [3, [6, 9]]] ``` Thus, the (i) methods with multiple arguments have a firm position. They have stronger motivation to exist as an independent concept, and accordingly, stronger motivation for their receiver and the arguments to be treated symmetrically. ---------------------------------------- Feature #19324: Enumerator.product => Enumerable#product https://bugs.ruby-lang.org/issues/19324#change-101194 * Author: zverok (Victor Shepelev) * Status: Open * Priority: Normal ---------------------------------------- I know it might be too late after introducing a feature and releasing a version, but I find `Enumerator.product` quite confusing, and can't find any justification in #18685. **Problem 1: It is `Array#product` but `Enumerator.product`** ```ruby [1, 2].product([4, 5]) # => [[1, 4], [1, 5], [2, 4], [2, 5]] # Usually, when we add methods to Enumerable/Enumerator which # already array had before, it is symmetric, say... [1, nil, 2, 3].compact #=> [1, 2, 3] [1, nil, 2, 3].lazy.compact.first(2) #=> [1, 2] # But not in this case: [1, 2].lazy.product([4, 5]).first(2) # undefined method `product' for #<Enumerator::Lazy: [1, 2]> (NoMethodError) # Because you "just" need to change it to: Enumerator.product([1, 2].lazy, [4, 5]).first(2) # => [[1, 4], [1, 5]] ``` No other method was "promoted" from Array this way And in general, I believe core methods tend to belong to the first object in the expression and not be free module methods, Elixir style. **Problem 2: It is one letter different from `Enumerator.produce`** I understand I might be biased here (as a person who proposed `produce`), and that method is not as popular (yet?) as I hoped, but still, two methods that do completely different things and differ by one letter, both being somewhat vague verbs (so it is easy to confuse them unless you did a lot of math and "product" is firmly set for set product in your head). I believe that EITHER of two problems would be concerning enough, but the combination of them seems to be a strong enough argument to make the change?.. (Maybe with graceful deprecation of module method in one next version, but, considering the Ruby 3.2 is just released, maybe vice versa, fix the problem in the next minor release?..) -- https://bugs.ruby-lang.org/