[ruby-core:111515] [Ruby master Bug#19278] Constructing subclasses of Data with positional arguments

29 Dec 2022

      Issue #19278 has been updated by sam.saffron (Sam Saffron).

Just going to be a bit more explicit here about the problem for future travelers (I know I am repeating but this is the most succinct way imo to show the issue)... 

```
Foo = Data.define :x

class Bar < Foo
  def initialize(*args, **kwargs)
    p args
    p kwargs
  end
 end

Bar.new(1)
# []
# {:x=>1}  
```

I am with tenderlove here, needing to reason about new -> initialize auto coercion is somewhat scary... 

I know this is a bucket of compromises given where we are at, but couldn't this just work correctly without coercion? 

``
class Foo
  attr_reader :x

  def initialize(*args, **kwargs)
    raise ArgumentError if args.length > 0 && kwargs.length > 0 
    raise ArgumentError if args.length > 1 || kwargs.length > 1
    raise ArgumentError if kwargs.length == 1 && !kwargs.key?(:x)

    if args.length > 0 
      x = args[0]
    else
      x = kwargs[:x]
    end
  end
end
```

----------------------------------------
Bug #19278: Constructing subclasses of Data with positional arguments
https://bugs.ruby-lang.org/issues/19278#change-100883

* Author: tenderlovemaking (Aaron Patterson)
* Status: Feedback
* Priority: Normal
* ruby -v: ruby 3.2.0 (2022-12-25 revision a528908271) [arm64-darwin22]
* Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN
----------------------------------------
I'd expect both of the following subclasses to work, but the subclass that uses positional parameters raises an exception:

```ruby
Foo = Data.define

class Bar < Foo
  def initialize foo:
    p foo
  end
end

class Baz < Foo
  def initialize foo
    p foo
  end
end

Bar.new foo: 1 # Prints 1
Baz.new 1    # Raises ArgumentError
```

I'd expect the subclass that uses positional arguments to work.

-- 
https://bugs.ruby-lang.org/