Re: [multi] Formal Review Begins

On 3/7/26 22:41, Andrzej Krzemienski via Boost wrote:
> sob., 7 mar 2026 o 10:58 Rainer Deyke via Boost <[email protected]>
> napisał(a):
> 
>> On 3/5/26 14:26, Matt Borland via Boost wrote:
>>> Multi is a modern C++ library that provides manipulation and access of
>> data in multidimensional arrays for both CPU and GPU memory.
>> I have my own multidimensional array type that I use extensively, so I
>> thought it would be interesting to compare my own efforts to the
>> proposed library.
>>
>> The proposed library uses an array-of-arrays model.  By contrast, my own
>> library uses an array-indexed-by-vector model.  This makes iteration a
>> lot more convenient with my type.  I do a lot of iteration in my own
>> code, so this is kind of a big deal.  Compare:
>>
>> My multi_array type:
>>
>>     multi_array<int, 2> a({5, 2});
>>     for (auto &element: a) {
>>       element = 5;
>>     }
>>     for (auto index: a.get_bounds()) {
>>       a[index] = get<0>(index) + get<1>(index) * 10;
>>     }
>>
>> The proposed library:
>>
>>     multi::array<int, 2> a({5, 2});
>>     for (auto &row: a) {
>>       for (auto &element: row) {
>>         element = 5;
>>       }
>>     }
>>     auto [rows, columns] = a.extensions();
>>     for (auto row_index: rows) {
>>       for (auto column_index: columns) {
>>         a[row_index][column_index] = row_index + column_index * 10;
>>       }
>>     }
>>
> 
> On the other hand, Boost.Multi is designed so that one usually doesn't need
> to do manual iteration. Your examples can be expressed as:
> 
> multi::array<int, 2> a({5, 2}, 5); // start with 5's
> std::ranges::fill(a.elements(), 6); // fill with 6's
> multi::array<int, 2> b = restricted([](int i, int j) { return i * j * 10;
> }, multi::extensions_t{5, 2});   // start with index-dependent values

That's great for these trivial examples, which I based on similar 
trivial examples in the Boost.Multi documentation.  Not so much if I'm 
trying to run a Gaussian blur on my data.  Or run a cellular automaton. 
Or even just render a 2D tile map on the screen.


-- 
Rainer Deyke - [email protected]

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