What is gsl::multi_span to be used for?

Question

The C++ core guidelines mention spans, not "multi-spans". But - I see that Microsoft's GSL implementation has a multi_span class

template <
    typename ValueType,
    std::ptrdiff_t FirstDimension,
    std::ptrdiff_t... RestDimensions
>
class multi_span { ... };

So, obviously this is some sort of a multi-dimensional version of gsl::span. But what is that supposed to mean? Why do we need this multi-dimensional span, or rather - when would we use it? I can't seem to find any documentation on this.

Answer 1

In short, it is a span over contiguous piece of memory, which represents multidimensional array.

Here is an example of use:

int data[6] = {0, 1, 2, 3, 4, 5};
multi_span<int, 2, 3> span{data, 6};
std::cout << span[1][1] << '\n'; //Outputs 4

From the linked source, it seems, that it also supports runtime bounds, but I am not sure about proper syntax for those.