$ bundle

$ gem install typed_model

Employee
  include ModelBase

  attribute :a_boolean, type: :boolean
  attribute :an_integer, type: :integer
  attribute :a_timestamp, type: :timestamp
  attribute :widget1, type: :map
  attribute :address, type: a_c
  attribute :addresses, seq_of: a_c
  attribute :colors, type: :seq
end

  # non-empty/nil sequence
  attribute :a_seq, type: :seq, :validations [:required]
  
  attribute :a_seq, seq_of: :string
  
  attribute :a_seq, seq_of: Address
  
  # sequence of string -> integer maps
  attribute :a_Seq, seq_of: [:string, :integer]
  
  attribute :a_seq, seq_of: { type: Adress, :validations [:some_validation] }

  # string -> string
  attribute :a_map, :map_of [:string, :integer]
  
  attribute :a_map, type: :map, validations: [:required]
  
  # map of maps
  attribute :map_of_maps, :map_of [:string, [:string, :integer]]
  
  # map of maps
  attribute :a_map, :map_of [{type: :string, validators: [:some_check]},
                             {type: Address, validators: [:required]},
                    :validators [:required]

    class Employee
        ...
        attribute :name, validations: [:my_validation]

        def assert_my_validation(attr)
          add_error(attr, 'some error')
        end
     end
     

    validator = Validator.new(:foo) do
       ['some error']
    end
    
    class Employee
       ...
       attribute :name, validations: [validator]