What is the Ruby equivalent of Python Dataclasses?

Question

What is the counterpart for the Python Dataclass in Ruby?

In Python it is possible to use dataclasses to tersely define a class without explicitly defining an initialiser / __init__ method for it.

Without dataclasses this would look like this in Python (including arg typing):

class myNewDog2:
    def __init__(fur_colour: str, weight: float, is_microchipped: bool, is_asleep:bool=False):      
      self.fur_colour = fur_colour
      self.weight = weight
      self.is_microchipped = is_microchipped
      self.is_asleep = is_asleep
   
my_dog = myDog("tri-colour", 19.52, True)

But can be reduced to a form not requiring writing args out twice, using dataclasses:

from dataclasses import dataclass

@dataclass
class myDog2:
    fur_colour: str
    weight: float
    is_microchipped: bool
    is_asleep: bool = False # Optional arg / defaults to False
   
my_dog = myDog("tri-colour", 19.52, True)

This is how an equivalent class definition looks like in Ruby:

class MyDog
  def initialize(fur_colour:, weight:, is_microchipped:, is_asleep: false)
    @fur_colour = fur_colour
    @weight = weight
    @is_microchipped = is_microchipped
    @is_asleep = is_asleep
  end 
end

How would I define this class in Ruby just as tersely as in Python? Is it possible to tell Ruby to fill in the blanks on the constructor based on only on a definition of the attributes I want the class to accept and maintain?

Answer 1

A similar way in Ruby seems to be the Data class, which allows you to define simple value object like this:

MyDog = Data.define(:fur_colour, :weight, :is_microchipped, :is_asleep)

And you can create instances with positional or keyword arguments like this:

my_dog = MyDog.new('tri-colour', 19.52, true, false) # or
my_dog = MyDog.new(fur_colour: 'tri-colour', weight: 19.52, is_microchipped: true, is_asleep: false)

Please note that the Data class doesn't support optional arguments, like the is_asleep argument in your example, yet (tested this with Ruby 3.3.1). You always need to provide the same number of arguments as defined.