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

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< cpp‎ | ranges
 
 
Ranges library
Range access
Range conversions
(C++23)
Range primitives



Dangling iterator handling
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Adaptors
Range adaptor objects
Range adaptor closure objects
Helper items
 
 
Defined in header <ranges>
template< ranges::input_range... Views >

    requires (ranges::view<Views> && ...) && (sizeof...(Views) > 0)

class zip_view : public ranges::view_interface<zip_view<Views...>>
(1) (since C++23)
namespace views {

    inline constexpr /*unspecified*/ zip = /*unspecified*/;

}
(2) (since C++23)
Call signature
template< ranges::viewable_range... Rs >

    requires /* see below */

constexpr auto zip( Rs&&... rs );
(since C++23)
Helper alias templates
template< class... Ts >
    using /*tuple-or-pair*/ = /* see description */;    // exposition only
(3) (since C++23)
Helper concepts
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> && ...));
(4) (since C++23)
Helper function templates
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));

}
(5) (since C++23)
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));

}
(6) (since C++23)
1) zip_view is a range adaptor that takes one or more views, and produces a view whose ith element is a tuple-like value consisting of the ith elements of all views. The size of produced view is the minimum of sizes of all adapted views.
2) views::zip is a customization point object.

When calling with no argument, views::zip() is expression-equivalent to auto(views::empty<std::tuple<>>).

Otherwise, views::zip(rs...) is expression-equivalent to ranges::zip_view<views::all_t<decltype((rs))>...>(rs...).
3) Let Ts be some pack of types, then /*tuple-or-pair*/<Ts...> denotes:

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

Contents

[edit] 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

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

[edit] 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)).

[edit] 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.

[edit] Member functions

constructs a zip_view
(public member function) [edit]
(C++23)
returns an iterator to the beginning
(public member function) [edit]
(C++23)
returns an iterator or a sentinel to the end
(public member function) [edit]
(C++23)
returns the number of elements. Provided only if each underlying (adapted) range satisfies sized_range.
(public member function) [edit]
Inherited from std::ranges::view_interface
(C++20)
Returns whether the derived view is empty. Provided if it satisfies sized_range or forward_range.
(public member function of std::ranges::view_interface<D>) [edit]
Returns whether the derived view is not empty. Provided if ranges::empty is applicable to it.
(public member function of std::ranges::view_interface<D>) [edit]
(C++20)
Returns the first element in the derived view. Provided if it satisfies forward_range.
(public member function of std::ranges::view_interface<D>) [edit]
(C++20)
Returns the last element in the derived view. Provided if it satisfies bidirectional_range and common_range.
(public member function of std::ranges::view_interface<D>) [edit]
Returns the nth element in the derived view. Provided if it satisfies random_access_range.
(public member function of std::ranges::view_interface<D>) [edit]

[edit] Deduction guides

[edit] Nested classes

(C++23)
the iterator type
(exposition-only member class template)
(C++23)
the sentinel type used when zip_view is not a common_range
(exposition-only member class template)

[edit] Helper templates

template< class... Views >

  inline constexpr bool enable_borrowed_range<ranges::zip_view<Views...>> =

    (ranges::enable_borrowed_range<Views> && ...);
(since C++23)

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

[edit] Notes

Feature-test macro Value Std Comment
__cpp_lib_ranges_zip 202110L (C++23)

std::ranges::zip_view,
std::ranges::zip_transform_view,
std::ranges::adjacent_view,
std::ranges::adjacent_transform_view

[edit] Example

Can be checked online on Compiler Explorer site.

#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);
}

Output:

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

[edit] See also

a view consisting of tuples of results of application of a transformation function to corresponding elements of the adapted views
(class template) (customization point object) [edit]
takes a view consisting of tuple-like values and a number N and produces a view of N'th element of each tuple
(class template) (range adaptor object) [edit]