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

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...>>

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

template< class F, ranges::viewable_range... Rs >
    requires /* see below */
constexpr auto zip_transform( F&& f, Rs&&... rs );

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

• FD models copy_constructible,
• FD& models regular_invocable, and
• std::invoke_result_t<FD&> is an object type,

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.

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
.

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

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

Data members

Typical implementations of zip_transform_view hold two non-static data members:

• an underlying view object of type InnerView (shown here as zip_ for exposition purposes only), and
• a wrapped invocable object of type movable-box<F> (shown here as fun_ for exposition purposes only).

Member functions

Deduction guides

Member types

Nested classes

Notes

Example

#include <array>
#include <iostream>
#include <list>
#include <ranges>
#include <vector>
 
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);
}

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

See also