Classes to / from JSON with inheritance and such (https://twitter.com/postmodern_mod3/status/1348330707420991497)

classes_to_and_from_json_with_inheritance_and_such.rb

# A potential way to deal with https://twitter.com/postmodern_mod3/status/1348330707420991497

# include it to get reasonable JSONability
module JsonCreatable
  def self.append_features(base)
    base.extend ClassMethods
    base.include InstanceMethods
  end

  module ClassMethods
    def json_create(hash)
      new **hash.transform_keys(&:intern)
    end
  end

  module InstanceMethods
    def initialize(*rest, json_class: nil, **kwrest, &block)
      super *rest, **kwrest, &block
    end

    def as_json
      hash = defined?(super) ? super : {}
      { **hash, json_class: self.class.name }
    end
  end
end


# Parent class
class User
  include JsonCreatable

  attr_reader :name

  def initialize(name:, **kwrest, &block)
    super **kwrest, &block
    @name = name
  end

  def as_json
    { **super, name: name }
  end
end

# Child class 
module Admin
  class User < ::User
    def initialize(is_admin:, **kwrest, &block)
      super **kwrest, &block
      @is_admin = is_admin
    end

    def admin?
      @is_admin
    end

    def as_json
      { **super, is_admin: admin? }
    end
  end
end

require 'json'

users = JSON.parse(<<~JSON, create_additions: true)
[ {"json_class":"User",        "name":"Josh"},
  {"json_class":"Admin::User", "name":"Marissa", "is_admin":true},
  {"json_class":"Admin::User", "name":"Dave",    "is_admin":false}
]
JSON

users
# => [#<User:0x00007ffaa79f4260 @name="Josh">,
#     #<Admin::User:0x00007ffaa79efda0 @is_admin=true, @name="Marissa">,
#     #<Admin::User:0x00007ffaa79ef968 @is_admin=false, @name="Dave">]

users.map(&:as_json)
# => [{:json_class=>"User", :name=>"Josh"},
#     {:json_class=>"Admin::User", :name=>"Marissa", :is_admin=>true},
#     {:json_class=>"Admin::User", :name=>"Dave", :is_admin=>false}]

users.map &:name # => ["Josh", "Marissa", "Dave"]
users.grep(Admin::User).map(&:admin?) # => [true, false]