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std::ranges...view::begin(3)   C++ Standard Libary  std::ranges...view::begin(3)

NAME
     std::ranges::cartesian_product_view::begin  -  std::ranges::cartesian_prod-
     uct_view::begin

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

	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_trans-
     form(ranges::begin,
	bases_));.
	2) Equivalent to return /*iterator*/<true>(__tuple_transform(ranges::be-
     gin,
	bases_));.

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

http://cppreference.com 	   2024.06.10	    std::ranges...view::begin(3)
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