cpp/ranges/cartesian product view/size

Returns the number of elements. The return type is an implementation-defined type.

Let be the underlying tuple of views, and  be the product of the sizes of all the ranges in.

@1-2@ Returns. The behavior is undefined if cannot be represented by the return type. Equivalent to:

Parameters
(none)

Return value
The number of elements, that is, the product of the sizes of all the underlying ranges.