module Data::_DataClass

Returns an array of member names of the data class:

Measure = Data.define(:amount, :unit)
Measure.members # => [:amount, :unit]

Constructors for classes defined with ::define accept both positional and keyword arguments.

Measure = Data.define(:amount, :unit)

Measure.new(1, 'km')
#=> #<data Measure amount=1, unit="km">
Measure.new(amount: 1, unit: 'km')
#=> #<data Measure amount=1, unit="km">

# Alternative shorter intialization with []
Measure[1, 'km']
#=> #<data Measure amount=1, unit="km">
Measure[amount: 1, unit: 'km']
#=> #<data Measure amount=1, unit="km">

All arguments are mandatory (unlike Struct), and converted to keyword arguments:

Measure.new(amount: 1)
# in `initialize': missing keyword: :unit (ArgumentError)

Measure.new(1)
# in `initialize': missing keyword: :unit (ArgumentError)

Note that Measure#initialize always receives keyword arguments, and that mandatory arguments are checked in initialize, not in new. This can be important for redefining initialize in order to convert arguments or provide defaults:

Measure = Data.define(:amount, :unit) do
  NONE = Data.define

  def initialize(amount:, unit: NONE.new)
    super(amount: Float(amount), unit:)
  end
end

Measure.new('10', 'km') # => #<data Measure amount=10.0, unit="km">
Measure.new(10_000)     # => #<data Measure amount=10000.0, unit=#<data NONE>>