class Protocol
  @@required_methods = []

  def self.required_method(method_name)
    @@required_methods << method_name
  end

  def self.required_methods
    return @@required_methods
  end
end

class SwiftClass
  @@protocols = []

  def self.inherit_protocol(protocol_name)
     protocol = Object.const_get(protocol_name)
     @@protocols << protocol
  end

  def self.inherit_protocols(*protocol_names)
    protocol_names.each do |protocol_name|
      inherit_protocol(protocol_name)
    end
  end

  def self.verify_conforms_to_protocols
    @@protocols.each do |protocol|
      if protocol.superclass != Protocol
        raise "ERROR: #{protocol} must be a subclass of Protocol"
      end
      if (missing_methods = self.missing_methods_for protocol).length > 0
        raise "nERROR: #{self} does not conform to protocol #{protocol}. nMISSING METHODS: #{missing_methods.join(", ")}"
      end
    end
  end

  def self.missing_methods_for(protocol)
    protocol.required_methods.select do |required_method|
      !self.method_defined? required_method
    end
  end

end

class SampleProtocol < Protocol
  required_method :number_of_sections_in
  required_method :number_of_rows_in_section
end

class SampleClass < SwiftClass
  inherit_protocols :SampleProtocol
  verify_conforms_to_protocols
end

ERROR: SampleClass does not conform to protocol SampleProtocol.
MISSING METHODS: number_of_sections_in, number_of_rows_in_section

class SampleClass < SwiftClass
  inherit_protocols :SampleProtocol

  def number_of_sections_in; end
  def number_of_rows_in_section; end

  verify_conforms_to_protocols
end

class SomeOtherProtocol < Protocol
   required_method :cell_for_row_at
end

ERROR: SampleClass does not conform to protocol SampleProtocol.
MISSING METHODS: cell_for_row_at