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

From cppreference.net
C++
Ranges library
Range adaptors
std::ranges::cartesian_product_view
Member functions
cartesian_product_view::begin
Deduction guides
Iterator
Member functions
Non-member functions
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_ ) ) ; .

Contents

Parameters

(none)

Return value

An iterator to the first element.

Example

Run this code 
#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

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)