Re: [multi] Formal Review Begins

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

Regards,
&rzej;
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