Named Parameters in Ruby Structs

Question

I\'m pretty new to Ruby so apologies if this is an obvious question.

I\'d like to use named parameters when instantiating a Struct, i.e. be able to specify which ite

Answer 1

Synthesizing the existing answers reveals a much simpler option for Ruby 2.0+:

class KeywordStruct < Struct
  def initialize(**kwargs)
    super(*members.map{|k| kwargs[k] })
  end
end

Usage is identical to the existing Struct, where any argument not given will default to nil:

Pet = KeywordStruct.new(:animal, :name)
Pet.new(animal: "Horse", name: "Bucephalus") # => #  
Pet.new(name: "Bob") # => # 

If you want to require the arguments like Ruby 2.1+'s required kwargs, it's a very small change:

class RequiredKeywordStruct < Struct
  def initialize(**kwargs)
    super(*members.map{|k| kwargs.fetch(k) })
  end
end

At that point, overriding initialize to give certain kwargs default values is also doable:

Pet = RequiredKeywordStruct.new(:animal, :name) do
  def initialize(animal: "Cat", **args)
    super(**args.merge(animal: animal))
  end
end

Pet.new(name: "Bob") # => #