From: "Eregon (Benoit Daloze)" Date: 2022-10-19T11:51:26+00:00 Subject: [ruby-core:110420] [Ruby master Feature#19063] Hash.new with non-value objects should be less confusing Issue #19063 has been updated by Eregon (Benoit Daloze). baweaver (Brandon Weaver) wrote in #note-29: > I would also be very positive of this change, potentially for Array as well, to make this visible to folks working in the language. For Array it doesn't make sense since the default value or block is evaluated only upon construction, and there is no need to keep it after. > What would be the impact of changing `inspect` in this way? I do not think it would be breaking, but would want others opinions on this. I'd think it'd break many programs which currently assume `eval hash.inspect` works, plus surprise people. Based on Jeremy's example in https://bugs.ruby-lang.org/issues/19063#note-21 I think there is nothing we can do here, there are valid usages of a mutable default value. It should be clear to any most programmers that `Hash.new(...)` only evaluates the value once (unlike `Hash.new { ... }`, and whether it `.dup` or so on each access is documented (it doesn't `.dup`). ---------------------------------------- Feature #19063: Hash.new with non-value objects should be less confusing https://bugs.ruby-lang.org/issues/19063#change-99731 * Author: baweaver (Brandon Weaver) * Status: Open * Priority: Normal ---------------------------------------- Related to #10713 and #2764. Ruby's `Hash.new` accepts either a block or a param for its default value. In the case of non-value objects this leads to unexpected behaviors: ```ruby bad_hash_with_array_values = Hash.new([]) good_hash_with_array_values = Hash.new { |h, k| h[k] = [] } ``` While, as @hsbt has said in the past, this is behaving as intended for the Ruby language it has caused a lot of confusion in the community over the years and is a known sharp-edge. My assertion is that this is not the intended behavior, and I cannot find a legitimate usecase in which someone intends for this to happen. More often new users to Ruby are confused by this behavior and spend a lot of time debugging. We must consider the impact to Ruby users, despite what the intent of the language is, and make the language more clear where possible. Given that, I have a few potential proposals for Ruby committers. ### Proposal 1: Do What They Meant When people use `Hash.new([])` they mean `Hash.new { |h, k| h[k] = [] }`. Can we make that the case that if you pass a mutable or non-value object that the behavior will be as intended using `dup` or other techniques? When used in the above incorrect way it is likely if not always broken code. ### Proposal 2: Warn About Unexpected Behavior As mentioned above, I do not believe there are legitimate usages of `Hash.new([])`, and it is a known bug to many users as they do not intend for that behavior. It may be worthwhile to warn people if they do use it. ### Proposal 3: Require Frozen or Values This is more breaking than the above, but it may make sense to require any value passed to `Hash.new` to either be `frozen` or a value object (e.g. `1` or `true`) ## Updating RuboCop Failing this, I am considering advocating for RuboCop and similar linters to warn people against this behavior as it is not intended in most to all cases: https://github.com/rubocop/rubocop/issues/11013 ...but as @ioquatix has mentioned on the issue it would make more sense to fix Ruby rather than put a patch on top of it. I would be inclined to agree with his assessment, and would rather fix this at a language level as it is a known point of confusion. ## Final Thoughts I would ask that maintainers consider the confusion that this has caused in the community, rather than asserting this "works as intended." It does work as intended, but the intended functionality can make Ruby more difficult for beginners. We should keep this in mind. -- https://bugs.ruby-lang.org/ Unsubscribe: