Transform a function `func` that returns tuples into a function that returns
    single values. Call a function `sink` on the unused values.

def sink_return(func, sink, splitter=None):  # pragma: no cover
    """Transform a function `func` that returns tuples into a function that returns
    single values. Call a function `sink` on the unused values.
    """

    def wrap(*args, **kwargs):
        output = func(*args, **kwargs)
        if splitter is None:
            to_keep, to_sink = output
        else:
            to_keep, to_sink = splitter(*output)
        sink(to_sink)
        return to_keep

    return wrap