    def is_bidirectional(self) -> bool:
        """
        Returns `True` if this encoder is bidirectional.  If so, we assume the forward direction
        of the encoder is the first half of the final dimension, and the backward direction is the
        second half.
        """
        raise NotImplementedError
Returns `True` if this encoder is bidirectional.  If so, we assume the forward direction
of the encoder is the first half of the final dimension, and the backward direction is the
second half.
allennlp/modules/seq2seq_encoders/seq2seq_encoder.py