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

From cppreference.com
< cpp‎ | ranges‎ | cartesian product view

constexpr iterator<false> begin() requires (!__simple_view<First> || ... || !__simple_view<Vs>); | (1) | (since C++23)
constexpr iterator<true> begin() const requires (ranges::range<const First> && ... && ranges::range<const Vs>); | (2) | (since C++23)

Returns an iterator to the first element of the `cartesian_product_view`.

Let `bases_` be the tuple of underlying views.

1) Equivalent to return /*iterator*/<false>(__tuple_transform(ranges::begin, bases_));.
2) Equivalent to return /*iterator*/<true>(__tuple_transform(ranges::begin, bases_));.

### Parameters

(none)

### Return value

Iterator to the first element.

### Example

Can be checked online with Compiler Explorer.

Run this code

    #include <array>
    #include <print>
    #include <ranges>
    #include <string_view>
    #include <tuple>
    using namespace std::literals;

    int main()
    {
        constexpr auto a = std::array{ "Curiously"sv, "Recurring"sv, "Template"sv, "Pattern"sv };

        constexpr auto v = std::ranges::cartesian_product_view(a[0], a[1], a[2], a[3]);

        constexpr std::tuple<char const&,
                             char const&,
                             char const&,
                             char const&> first { *v.begin() };

        std::println("{}{}{}{}",
                     std::get<0>(first),
                     std::get<1>(first),
                     std::get<2>(first),
                     std::get<3>(first));
    }

Output:

    CRTP

### See also

end (C++23) | returns an iterator or a sentinel to the end (public member function)
ranges::begin (C++20) | returns an iterator to the beginning of a range (customization point object)

Retrieved from "https://en.cppreference.com/mwiki/index.php?title=cpp/ranges/cartesian_product_view/begin&oldid=145088"