def METHOD_NAME(cls, dataset: torch.utils.data.Dataset, *args, **kwargs):
    """Return the source and target datasets for masked LM training."""
    dataset = LRUCacheDataset(dataset)
    return (
        LRUCacheDataset(cls(dataset, *args, **kwargs, return_masked_tokens=False)),
        LRUCacheDataset(cls(dataset, *args, **kwargs, return_masked_tokens=True)),
    )