# std::ranges::cartesian_product_view<First, Vs...>::size

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< cpp‎ | ranges‎ | cartesian product view

constexpr /* see description */ size() requires __cartesian_product_is_sized<First, Vs...>; | (1) | (since C++23)
constexpr /* see description */ size() const requires __cartesian_product_is_sized<const First, const Vs...>; | (2) | (since C++23)

Returns the number of elements. The return type is an implementation-defined `unsigned-integer-like` type U.

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

1-2) Returns prod. The behavior is undefined if prod cannot be represented by the return type U.

Equivalent to:

    return [&]<std::size_t... Is>(std::index_sequence<Is...>)
    {
        auto prod = static_cast<U>(1);
        prod = (static_cast<U>(ranges::size(std::get<Is>(bases_))) * ...);
        return prod;
    }
    (std::make_index_sequence<1U + sizeof...(Vs)>{});

### Parameters

(none)

### Return value

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

### Notes

The return type is the smallest `unsigned-integer-like` type that is sufficiently wide to store the product of the maximum sizes of all the underlying ranges, if such a type exists.

### Example

Can be checked online with Compiler Explorer.

Run this code

    #include <ranges>

    int main()
    {
        constexpr static auto w = { 1 };
        constexpr static auto x = { 2, 3 };
        constexpr static auto y = { 4, 5, 6 };
        constexpr static auto z = { 7, 8, 9, 10, 11, 12, 13 };
        constexpr auto v = std::ranges::cartesian_product_view(w, x, y, z);
        static_assert(v.size() == w.size() * x.size() * y.size() * z.size() and v.size() == 42);
    }

### See also

ranges::size (C++20) | returns an integer equal to the size of a range (customization point object)
ranges::ssize (C++20) | returns a signed integer equal to the size of a range (customization point object)

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