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std::ranges::views::zip_transform, std::ranges::zip_transform_view

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< cpp‎ | ranges
 
 
Ranges library
Range access
Range conversions
(C++23)
Range primitives
Dangling iterator handling
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Defined in header <ranges>
template< std::copy_constructible F, ranges::input_range... Views >

    requires (ranges::view<Views> && ...) && (sizeof...(Views) > 0) &&
              std::is_object_v<F> && std::regular_invocable<
                  F&, ranges::range_reference_t<Views>...> &&
              /*can-reference*/<std::invoke_result_t<
                  F&, ranges::range_reference_t<Views>...>>
class zip_transform_view

     : public ranges::view_interface<zip_transform_view<F, Views...>>
(1) (since C++23)
namespace views {

    inline constexpr /*unspecified*/ zip_transform = /*unspecified*/;

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

    requires /* see below */

constexpr auto zip_transform( F&& f, Rs&&... rs );
(since C++23)
1) zip_transform_view is a range adaptor that takes an invocable object and one or more views, and produces a view whose ith element is the result of applying the invocable object to the ith elements of all views.
A type T models the exposition-only concept can-reference if and only if T& is a valid type.
2) views::zip_transform is a customization point object.

When calling with one argument f, let FD be std::decay_t<decltype(f)>, if:

then views::zip_transform(f) is expression-equivalent to ((void)f, auto(views::empty<std::decay_t<std::invoke_result_t<FD&>>>)). Otherwise, the call to views::zip_transform is ill-formed.

When calling with more than one arguments f and rs..., views::zip_transform(f, rs...) is expression-equivalent to ranges::zip_transform_view(f, rs...).

zip_transform_view models the concepts random_access_range, bidirectional_range, forward_range, input_range, common_range, and sized_range when the underlying ranges::zip_view<Views...> models respective concepts.

Contents

[edit] Customization point objects

The name views::zip_transform 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_transform_fn.

All instances of __zip_transform_fn are equal. The effects of invoking different instances of type __zip_transform_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_transform 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_transform above, __zip_transform_fn models

Otherwise, no function call operator of __zip_transform_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_transform_view hold two non-static data members:

  • an underlying view object of type ranges::zip_view<Views...> (shown here as zip_ for exposition only), and
  • a wrapped invocable object of type copyable-box<F> (shown here as fun_ for exposition only).

[edit] Member functions

constructs a zip_transform_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 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 the underlying zip_view is not a common_range
(exposition-only member class template)

[edit] Notes

Feature testing macro: __cpp_lib_ranges_zip

[edit] Example

#include <list>
#include <array>
#include <ranges>
#include <vector>
#include <iostream>
 
void print(auto const rem, auto const& r) {
    for (std::cout << rem; auto const& e : r)
        std::cout << e << ' ';
    std::cout << '\n';
}
 
int main() {
    auto v1 = std::vector<float>{1, 2, 3};
    auto v2 = std::list<short>{1, 2, 3, 4};
    auto v3 = std::to_array({1, 2, 3, 4, 5});
 
    auto add = [](auto a, auto b, auto c) { return a + b + c; };
 
    auto sum = std::views::zip_transform(add, v1, v2, v3);
 
    print("v1:  ", v1);
    print("v2:  ", v2);
    print("v3:  ", v3);
    print("sum: ", sum);
}

Output:

v1:  1 2 3 
v2:  1 2 3 4 
v3:  1 2 3 4 5 
sum: 3 6 9

[edit] See also

a view consisting of tuples of references to corresponding elements of the adapted views
(class template) (customization point object) [edit]
a view of a sequence that applies a transformation function to each element
(class template) (range adaptor object) [edit]