Issue #19301 has been updated by zverok (Victor Shepelev). Status changed from Open to Rejected See discussions in #19278 and #19280. This is a conscious decision of `Data.new` converting all arguments to keyword ones, made for ease of providing default values or preprocessing of arguments, without caring about the form they were passed in: ```ruby DataExample = Data.define(:one, :two) do def initialize(one:, two: 0) = super(one: one.to_i, two: two.to_i) end DataExample.new('1') # => #<data DataExample one=1, two=0> DataExample.new(1) # => #<data DataExample one=1, two=0> DataExample.new(one: '1') # => #<data DataExample one=1, two=0> DataExample.new(one: '1', two: '2') # => #<data DataExample one=1, two=2> ``` This would be very hard to achieve if `Data` (like `Struct`) would convert arguments in `#initialize`. (You can try yourself with a `Struct` to define the `#initialize` which does the same.) I will work on improving the implicitness of this in the documentation, though. I am not sure about your `DemoExample` which raises (I can't see anything called `DemoExample` in your definitions). This works for me, if that was meant: ```ruby DataExample[1, 2] #=> #<data DataExample one=1, two=2> ``` To see (for metaprogramming, say) "all parameters that `Data.new` accepts", you can do this: ```ruby DataExample.method(:new).parameters #=> [[:rest]] ``` ...which would be like Struct's `[[:rest]]` (and not that informative, but that's typically this for C-defined methods.) ---------------------------------------- Bug #19301: Fix Data class to report keyrest instead of rest parameters https://bugs.ruby-lang.org/issues/19301#change-100952 * Author: bkuhlmann (Brooke Kuhlmann) * Status: Rejected * Priority: Normal * ruby -v: ruby 3.2.0 (2022-12-25 revision a528908271) [arm64-darwin22.2.0] * Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN ---------------------------------------- ## Overview Hello and Happy New Year. 👋 With the new `Data` class, I'm seeing a discrepancy in parameter behavior compared to a `Struct`. I understand the original `Data` [feature](https://bugs.ruby-lang.org/issues/16122) request made design choices to only accept keyword arguments for the `#initialize` method but reporting `[[rest]]` parameters seems misleading to me because it doesn't share the more flexible `Struct#initialize` behavior and would like to request `Data#initialize` answer `[[keyrest]]` for parameters for improved metaprogramming accuracy. ## Steps to Recreate To reproduce, consider the following: ``` ruby DataExample = Data.define :one, :two StructExample = Struct.new :one, :two argument_array = [one: 1, two: 2] argument_hash = {one: 1, two: 2} puts "Data (parameters): #{DataExample.method(:initialize).parameters}" puts "Struct (parameters): #{StructExample.method(:initialize).parameters}" puts "Data (argument hash): #{DataExample[**argument_hash]}" puts "Struct (argument array): #{StructExample[*argument_array]}" puts "Struct (argument hash): #{StructExample[**argument_hash]}" ``` The above will output the following: ``` Data (parameters): [[:rest]] Struct (parameters): [[:rest]] Data (argument hash): #<data DataExample one=1, two=2> Struct (argument array): #<struct StructExample one={:one=>1, :two=>2}, two=nil> Struct (argument hash): #<struct StructExample one=1, two=2> ``` The `Struct` class -- as far as I know -- has always reported `[[rest]]` parameters even though it can accept positional or keyword arguments without error. ...but *this is definitely not the case with* the `Data` class which can be seen when running the following modification to the above: ``` ruby DemoExample[*argument_array] # missing keyword: :two (ArgumentError) ``` The above clearly betrays the `[[rest]]` parameters response (granted a `Struct` is slightly devious too but at least happily accepts positional or keyword arguments). With this in mind, could `Data#initalize` be fixed to at least report `[[keyrest]]` so we'd have a better chance of metaprogramming the correct argument format based on the `#parameters` response for initializing a `Data` instance correctly? Thanks. 🙇🏻♂️ ## Environment `ruby 3.2.0 (2022-12-25 revision a528908271) [arm64-darwin22.2.0]` -- https://bugs.ruby-lang.org/