def __init__(self, definition):
super(Struct, self).__init__()<EOL>self.definition = definition<EOL>
Args:
    definition (class): A generated class representing a Stone struct
        from a spec. Must have a _fields_ attribute with the following
        structure:

        _fields_ = [(field_name, validator), ...]

        where
            field_name: Name of the field (str).
            validator: Validator object.