presto-spi/src/main/java/io/prestosql/spi/block/SingleRowBlockWriter.java/SingleRowBlockWriter/toString
class SingleRowBlockWriter:    @Override
    public String toString()
    {
        if (!fieldBlockBuilderReturned) {
            return format("SingleRowBlockWriter{numFields=%d, fieldBlockBuilderReturned=false, positionCount=%d}", fieldBlockBuilders.length, getPositionCount());
        }
        else {
            return format("SingleRowBlockWriter{numFields=%d, fieldBlockBuilderReturned=true}", fieldBlockBuilders.length);
        }
    }