presto-spi/src/main/java/io/prestosql/spi/block/LazyBlock.java/LazyBlock/getPositions
class LazyBlock:    @Override
    public Block getPositions(int[] positions, int offset, int length)
    {
        if (isLoaded()) {
            return getBlock().getPositions(positions, offset, length);
        }
        checkArrayRange(positions, offset, length);
        return new LazyBlock(length, new PositionLazyBlockLoader(lazyData, positions, offset, length));
    }