def concat(
        cls,
        indexes: Sequence[Self],
        dim: Hashable,
        positions: Iterable[Iterable[int]] | None = None,
    ) -> Self:
        """Create a new index by concatenating one or more indexes of the same
        type.

        Implementation is optional but required in order to support
        ``concat``. Otherwise it will raise an error if the index needs to be
        updated during the operation.

        Parameters
        ----------
        indexes : sequence of Index objects
            Indexes objects to concatenate together. All objects must be of the
            same type.
        dim : Hashable
            Name of the dimension to concatenate along.
        positions : None or list of integer arrays, optional
            List of integer arrays which specifies the integer positions to which
            to assign each dataset along the concatenated dimension. If not
            supplied, objects are concatenated in the provided order.

        Returns
        -------
        index : Index
            A new Index object.
        """
        raise NotImplementedError()
Create a new index by concatenating one or more indexes of the same
        type.

        Implementation is optional but required in order to support
        ``concat``. Otherwise it will raise an error if the index needs to be
        updated during the operation.

        Parameters
        ----------
        indexes : sequence of Index objects
            Indexes objects to concatenate together. All objects must be of the
            same type.
        dim : Hashable
            Name of the dimension to concatenate along.
        positions : None or list of integer arrays, optional
            List of integer arrays which specifies the integer positions to which
            to assign each dataset along the concatenated dimension. If not
            supplied, objects are concatenated in the provided order.

        Returns
        -------
        index : Index
            A new Index object.
        
xarray/core/indexes.py