def index(self, element: Element) -> int:
        """
        Return the index in the array of the first item whose value is element.
        It is an error if there is no such item.

        >>> element = String('hello')
        >>> array = Array(content=[element])
        >>> array.index(element)
        0
        """

        from refract.refraction import refract
        return self.content.index(refract(element))