inputs.rb

class DateOfBirth
  include Virtus.model

  attribute :year, Integer
  attribute :month, Integer
  attribute :year, Integer

  def to_s
    Date.new year, month, day
  end
end

class Person
  include Virtus.model

  attribute :dob, DateOfBirth
end

class Salary
  include Virtus.model

  attribute :amount
  attribute :frequency
end

class Contribution
  include Virtus.model
  attribute :value
  attribute :frequency

  #
  # Let the object tell us what data type we are using
  #
  # Need activesupport to do this bit of magic
  #
  def datatype
    __model__.snakecase.split '_'
  end
end

class ContributionPercentage < Contribution
end

class ContributionCurrency < Contribution
end

class Pot
  attribute :value
end

class Inputs
  include Virtus.model
  include ActiveModel::Model

  attribute :person, Person
  attribute :salary, Salary

  attribute :employee_contribution, Contribution
  attribute :employer_contribution, Contribution

  attribute :contribution_pot, ContributionPot

  attribute :target_income, TargetIncome
  attribute :delay_contribution, DelayContribution

  attribute :pots, Array[Pot]
end

input = Input.new params

input.valid?
input.errors
input.attributes
input.employee_contribution.valid?