なんとなくプロトコル定義からデータ構造を自動生成するためのひな形

type.rb

require 'hashie'
require 'pry'

class CoercionError < StandardError; end

class ValueCoercer
  def initialize(name, klass)
    @name = name
    @klass = klass
  end
  def coerce(value)
    case value
    when @klass
      value
    else
      raise CoercionError, "#{@name} is not #{@klass}: '#{value}'"
    end
  end
end

class Item < Hashie::Dash
  property :name, required: true
  property :price, required: true

  include Hashie::Extensions::Coercion

  coerce_key :name,  ValueCoercer.new(:name, String)
  coerce_key :price, ValueCoercer.new(:price, Integer)
end

class User < Hashie::Dash
  property :id, required: true
  property :name, required: true
  property :item, required: true

  include Hashie::Extensions::Coercion

  coerce_key :id,   ValueCoercer.new(:id, Integer)
  coerce_key :name, ValueCoercer.new(:name, String)
  coerce_key :item, Item
end

# ↑この辺まで自動生成


u1 = User.new(id: 1, name: 'hoge', item: {name: 'つえ', price: 10}) #

binding.pry

begin
  u2 = User.new(id: 'illegal', name: 'hoge', item: {name: 'つえ', price: 10}) # raises CoercionError
rescue
  p $!
  binding.pry
end