Selecting elements of nested array

[kruglov-dmitry]

Given table:

CREATE TABLE IF NOT EXISTS maps.multiarray
(
    `arr` Array(Array(UInt64))
)
ENGINE = Memory;

with single row:

INSERT INTO maps.multiarray VALUES ([[0,1,2,3,4,5], [100, 200], [10,20, 50, 70]]);

I am trying to run select, using code similar to what is written at test:

string SELECT_QUERY = "SELECT arr FROM maps.multiarray";
client.Select(SELECT_QUERY, [](const Block& block)
{
    if (block.GetRowCount() == 0) {
         return;
    }

    for (size_t c = 0; c < block.GetRowCount(); ++c) {
        auto col = block[0]->As<ColumnArray>()->GetAsColumn(c);
	cout << col->Size() << endl;
	cout << "[";
	for (size_t i = 0; i < col->Size(); ++i) {
	      auto col2 = col->As<ColumnArray>()->GetAsColumn(i);
              for (size_t j = 0; j < col2->Size(); ++j) {
		     cout << (int)(*col2->As<ColumnUInt64>())[j];
                     if (j + 1 != col2->Size()) {
			cout << " ";
                     }
               }
       }
       std::cout << "]" << std::endl;
    }
});

And as a result got only this kind of output:

1
[0]

While I was expecting to have something like that:

5
[0 1 2 3 4 5]
2
[100 200]
4
[10 20 50 70]

I've tried to access exact same table using client in other languages and it seems to work as expected:

from clickhouse_driver import connect
conn = connect('clickhouse://localhost')
cursor = conn.cursor()
cursor.execute('SELECT * FROM maps.multiarray')
cursor.fetchall()
[([[0, 1, 2, 3, 4, 5], [100, 200], [10, 20, 50, 70]],)]

I've also saw similar issue within alternative(?) implementation - here.

I can sort of work-around it by issuing first SELECT length(arr) FROM maps.multiarray with subsequent series of calls select arrayElement(arr, idx) from maps.multiarray;

But it is not clear is it limitation of existing client or I just miss something important in my implementation?