std::ranges:: views:: adjacent_transform, std::ranges:: adjacent_transform_view, std::ranges:: views:: pairwise_transform

From cppreference.com
C++
Ranges library
Range adaptors
(C++23) (C++23)
(C++23)
adjacent_transform_view views::adjacent_transform
(C++23) (C++23)
views::pairwise_transform
(C++23)
(C++23) (C++23)
(C++23) (C++23)
(C++23) (C++23)
(C++23) (C++23)
(C++23) (C++23)

std::ranges::adjacent_transform_view
Member functions
Iterator
Member functions
Non-member functions
Sentinel
Member functions
Non-member functions
Defined in header <ranges>
template < ranges:: forward_range V, std:: move_constructible F, std:: size_t N >

requires ranges:: view < V > && ( N > 0 ) && std:: is_object_v < F > &&
std:: regular_invocable < F & ,
/*REPEAT*/ ( ranges:: range_reference_t < V > , N ) ... > &&
/*can-reference*/ < std:: invoke_result_t < F & ,
/*REPEAT*/ ( ranges:: range_reference_t < V > , N ) ... >>
class adjacent_transform_view

: public ranges:: view_interface < adjacent_transform_view < V, F, N >>
(1) (since C++23)
namespace views {

template < std:: size_t N >
constexpr /* unspecified */ adjacent_transform = /* unspecified */ ;

}
(2) (since C++23)
namespace views {

inline constexpr auto pairwise_transform = adjacent_transform < 2 > ;

}
(3) (since C++23)
Call signature
template < ranges:: viewable_range R, class F >

requires /* see below */

constexpr ranges:: view auto adjacent_transform < N > ( R && r, F && fun ) ;
(since C++23)
template < class F >
constexpr /*range adaptor closure*/ adjacent_transform < N > ( F && fun ) ;
(since C++23)
1) adjacent_transform_view is a range adaptor that takes a view and an invocable object fun , and produces a view whose i th element is a value that is the result of applying fun to each element in [ i , i + N ) of the original view. F always has arity N .
Let S be the size of the original view. Then the size of produced view is:
  • S - N + 1 , if S >= N ,
  • ​ 0 ​ otherwise, and the resulting view is empty.
2) The name views :: adjacent_transform < N > denotes a RangeAdaptorObject . Given subexpressions e and f , and a constant expression N , the expression views :: adjacent_transform < N > ( e, f ) is expression-equivalent to:
3) The name views :: pairwise_transform denotes a RangeAdaptorObject that behaves exactly as views :: adjacent_transform < 2 > . In particular, the arity of F is also 2 and fun is a binary invocable object.

adjacent_transform_view always models forward_range , and models bidirectional_range , random_access_range , or sized_range , if adapted view type models the corresponding concept.

Member functions

constructs a adjacent_transform_view
(public member function)
returns an iterator to the beginning
(public member function)
returns an iterator or a sentinel to the end
(public member function)
returns the number of elements. Provided only if the underlying (adapted) range satisfies sized_range .
(public member function)
Inherited from std::ranges::view_interface
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> )
(C++23)
returns a constant iterator to the beginning of the range.
(public member function of std::ranges::view_interface<D> )
(C++23)
returns a sentinel for the constant iterator of the range.
(public member function of std::ranges::view_interface<D> )
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> )
returns the first element in the derived view. Provided if it satisfies forward_range .
(public member function of std::ranges::view_interface<D> )
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> )
returns the n th element in the derived view. Provided if it satisfies random_access_range .
(public member function of std::ranges::view_interface<D> )

Deduction guides

(none)

Member types

Member type Definition
InnerView (private) ranges:: adjacent_view < V, N > .
( exposition-only member type* )
inner_iterator (private)
inner_sentinel (private)

Data members

Member name Definition
fun_ (private) /*movable-box*/ < F >
( exposition-only member object* )
inner_ (private) ranges:: adjacent_view < V,N >
( exposition-only member object* )

Nested classes

the iterator type
( exposition-only member class template* )
the sentinel type used when adjacent_transform_view is not a common_range
( exposition-only member class template* )

Notes

views :: adjacent_transform only accepts foward ranges even when N is 0 .

Feature-test macro Value Std Feature
__cpp_lib_ranges_zip 202110L (C++23) ranges:: zip_view ,
ranges:: zip_transform_view ,
ranges:: adjacent_view ,
ranges::adjacent_transform_view

Example

Run this code 
#include <array>
#include <iostream>
#include <ranges>
 
int main()
{
    constexpr static std::array data{1, 2, 3, 4, 5, 6};
    constexpr int window{3};
 
    auto Fun = [](auto... ints) { return (... + ints); };
    // Alternatively, the Fun could be any ternary (if window == 3) callable, e.g.:
    // auto Fun = [](int x, int y, int z) { return x + y + z; };
 
    constexpr auto view = data | std::views::adjacent_transform<window>(Fun);
 
    static_assert(
        view.size() == (data.size() - window + 1)
        && std::array{6, 9, 12, 15}
        == std::array{view[0], view[1], view[2], view[3]}
        && view[0] == Fun(data[0], data[1], data[2])
        && view[1] == Fun(data[1], data[2], data[3])
        && view[2] == Fun(data[2], data[3], data[4])
        && view[3] == Fun(data[3], data[4], data[5])
    );
 
    for (int x : view)
        std::cout << x << ' ';
    std::cout << '\n';
}

Output: 

6 9 12 15

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior
LWG 4098 C++23 views :: adjacent_transform < 0 > used to accept input-only ranges made rejected

References

  • C++23 standard (ISO/IEC 14882:2024):
  • 26.7.27 Adjacent transform view [range.adjacent.transform]

See also

(C++23)
a view consisting of tuples of references to adjacent elements of the adapted view
(class template) (range adaptor object)
(C++20)
a view of a sequence that applies a transformation function to each element
(class template) (range adaptor object)
(C++23)
a view consisting of results of application of a transformation function to corresponding elements of the adapted views
(class template) (customization point object)
(C++20)
applies a function to a range of elements
(algorithm function object)
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