std::ranges::views::zip, std::ranges::zip_view

template< ranges::input_range... Views >
    requires (ranges::view<Views> && ...) && (sizeof...(Views) > 0)
class zip_view : public ranges::view_interface<zip_view<Views...>>

namespace views {
    inline constexpr /*unspecified*/ zip = /*unspecified*/;
}

template< ranges::viewable_range... Rs >
    requires /* see below */
constexpr auto zip( Rs&&... rs );

template< class... Ts >
    using /*tuple-or-pair*/ = /* see description */;    // exposition only

template< class... Rs >
  concept /*zip-is-common*/ =    // exposition only
    (sizeof...(Rs) == 1 && (ranges::common_range<Rs> && ...))
    ||
    (!(ranges::bidirectional_range<Rs> && ...) && (ranges::common_range<Rs> && ...))
    ||
    ((ranges::random_access_range<Rs> && ...) && (ranges::sized_range<Rs> && ...));

template< class F, class Tuple >
constexpr auto /*tuple-transform*/( F&& f, Tuple&& tuple ) {    // exposition only
  return std::apply([&]<class... Ts>(Ts&&... elements) {
    return /*tuple-or-pair*/<std::invoke_result_t<F&, Ts>...>(
      std::invoke(f, std::forward<Ts>(elements))...
    );
  }, std::forward<Tuple>(tuple));
}

template< class F, class Tuple >
constexpr void /*tuple-for-each*/( F&& f, Tuple&& tuple ) {    // exposition only
  std::apply([&]<class... Ts>(Ts&&... elements) {
    (std::invoke(f, std::forward<Ts>(elements)), ...);
  }, std::forward<Tuple>(tuple));
}

• std::pair<Ts...>, if sizeof...(Ts) is 2,
• std::tuple<Ts...> otherwise.

zip_view always models input_range, and models forward_range, bidirectional_range, random_access_range, or sized_range if all adapted view types model the corresponding concept.

zip_view models common_range if.

• sizeof...(Views) is equal to 1, and the only adapted view type models common_range, or
• at least one adapted view type does not model bidirectional_range, and every adapted view type models common_range, or
• every adapted view type models both random_access_range and sized_range.

Customization point objects

The name views::zip denotes a customization point object, which is a const function object of a literal semiregular class type. For exposition purposes, the cv-unqualified version of its type is denoted as __zip_fn.

All instances of __zip_fn are equal. The effects of invoking different instances of type __zip_fn on the same arguments are equivalent, regardless of whether the expression denoting the instance is an lvalue or rvalue, and is const-qualified or not (however, a volatile-qualified instance is not required to be invocable). Thus, views::zip can be copied freely and its copies can be used interchangeably.

Given a set of types Args..., if std::declval<Args>()... meet the requirements for arguments to views::zip above, __zip_fn models
.

• std::invocable<__zip_fn, Args...>,
• std::invocable<const __zip_fn, Args...>,
• std::invocable<__zip_fn&, Args...>, and
• std::invocable<const __zip_fn&, Args...>.
  

Otherwise, no function call operator of __zip_fn participates in overload resolution.

Expression-equivalent

Expression e is expression-equivalent to expression f, if.

• e and f have the same effects, and
• either both are constant subexpressions or else neither is a constant subexpression, and
• either both are potentially-throwing or else neither is potentially-throwing (i.e. noexcept(e) == noexcept(f)).

Data members

Typical implementations of zip_view hold only one non-static data member: a std::tuple<Views...> holding all adapted view objects.

For the purpose of exposition, the view objects in that std::tuple are shown as vs_... here.

Member functions

Deduction guides

Nested classes

Helper templates

template< class... Views >
  inline constexpr bool enable_borrowed_range<ranges::zip_view<Views...>> =
    (ranges::enable_borrowed_range<Views> && ...);

This specialization of ranges::enable_borrowed_range makes zip_view satisfy borrowed_range when each underlying view satisfies it.

Notes

Example

#include <list>
#include <array>
#include <tuple>
#include <ranges>
#include <vector>
#include <string>
#include <iostream>
 
void print(auto const rem, auto const& range) {
   for (std::cout << rem; auto const& elem : range)
     std::cout << elem << ' ';
   std::cout << '\n';
}
 
int main() {
    auto x = std::vector{1, 2, 3, 4};
    auto y = std::list<std::string>{"α", "β", "γ", "δ", "ε"};
    auto z = std::array{'A', 'B', 'C', 'D', 'E', 'F'};
 
    print("Source views:", "");
    print("x: ", x);
    print("y: ", y);
    print("z: ", z);
 
    print("\nzip(x,y,z):", "");
    for (std::tuple<int&, std::string&, char&> elem : std::views::zip(x, y, z)) {
        std::cout << std::get<0>(elem) << ' '
                  << std::get<1>(elem) << ' '
                  << std::get<2>(elem) << '\n';
 
        std::get<char&>(elem) += ('a' - 'A'); // modifies the element of z
    }
 
    print("\nAfter modification, z: ", z);
}

Source views:
x: 1 2 3 4
y: α β γ δ ε
z: A B C D E F
 
zip(x,y,z):
1 α A
2 β B
3 γ C
4 δ D
 
After modification, z: a b c d E F

See also