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

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

An iterator to the first element.

Example

#include <array>
#include <format>
#include <iostream>
#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::cout << std::format("{}{}{}{}{}",
                             std::get<0>(first),
                             std::get<1>(first),
                             std::get<2>(first),
                             std::get<3>(first),
                             '\n');
}

Output:

CRTP

See also

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

© cppreference.com
Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.
https://en.cppreference.com/w/cpp/ranges/cartesian_product_view/begin