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Difference between revisions of "cpp/ranges/stride view"

From cppreference.com
< cpp‎ | ranges
m (→‎Member functions: +ad hoc `stride()` row (dsc is unnecessary))
m (fix: size=s/n+s%n?1:0)
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}}
 
}}
 
{{dcl h|Helper templates}}
 
{{dcl h|Helper templates}}
−
<!-- TODO: show or add links to: __simple_view , __div_ceil, __maybe_const, __to_unsigned_like, __see_below :) -->
+
<!-- TODO: show or add links to: __simple_view , __div_ceil, __maybe_const, __to_unsigned_like -->
 
{{dcl end}}
 
{{dcl end}}
  
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@@ Let {{tt|''S''}} be the size of the original view. Then the size of produced view is:
 
@@ Let {{tt|''S''}} be the size of the original view. Then the size of produced view is:
−
* {{c|S / n}}, if {{c|1=S >= n}}; otherwise,
+
* {{c|(S / n) + (S % n ? 1 : 0)}}, if {{c|1=S >= n}}; otherwise,
 
* {{c|1}}, if {{c|S > 0}}; otherwise,
 
* {{c|1}}, if {{c|S > 0}}; otherwise,
 
* {{c|0}}, and the resulting view is empty.
 
* {{c|0}}, and the resulting view is empty.
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{{tt|stride_view}} always models {{lconcept|input_range}}, and models {{lconcept|forward_range}}, {{lconcept|bidirectional_range}}, {{lconcept|random_access_range}}, and/or {{lconcept|sized_range}}, if adapted {{lconcept|view}} type {{c|V}} models the corresponding concept.
 
{{tt|stride_view}} always models {{lconcept|input_range}}, and models {{lconcept|forward_range}}, {{lconcept|bidirectional_range}}, {{lconcept|random_access_range}}, and/or {{lconcept|sized_range}}, if adapted {{lconcept|view}} type {{c|V}} models the corresponding concept.
−
<!-- {{tt|stride_view}} models {{lconcept|common_range}} if -->
+
{{c|stride_view<V>}} models {{lconcept|common_range}} whenever the underlying view {{c|V}} does.
−
<!-- {{cpp/ranges/cpo|views|stride}} -->
+
 
{{cpp/expr-eq}}
 
{{cpp/expr-eq}}
  
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}
 
}
 
|output=
 
|output=
−
1 4 7 10  
+
1 4 7 10
−
10 7 4 1  
+
10 7 4 1
−
12 9 6 3  
+
12 9 6 3
 
password
 
password
 
}}
 
}}

Revision as of 13:16, 9 November 2022

 
C++
 
Ranges library
Range adaptors
 
std::ranges::stride_view
Member functions
Deduction guides
Iterator
Member functions
Non-member functions
 
Defined in header <ranges>
template< ranges::input_range V >

    requires ranges::view<V>
class stride_view :

    public ranges::view_interface<stride_view<V>>
 (1) (since C++23)
namespace views {

    inline constexpr /* unspecified */ stride = /* unspecified */;

}
 (2) (since C++23)
Call signature
template< ranges::viewable_range R >
constexpr ranges::view auto stride( R&& r, ranges::range_difference_t<V> n );
 (since C++23)
template< ranges::forward_range V >

    requires ranges::view<V>

constexpr __range_adaptor_closure stride( ranges::range_difference_t<V> n );
 (since C++23)
Helper templates
1) stride_view is a range adaptor that takes a view and a number n and produces a view, that consists of elements of the original view by advancing over n elements at a time. This means that each mth element of the produced view is (n * i)th element of the original view, for some non-negative index i. The elements of the original view, whose "index" is not a multiple of n, are not present in the produced view.
Let S be the size of the original view. Then the size of produced view is:
  • (S / n) + (S % n ? 1 : 0), if S >= n; otherwise,
  • 1, if S > 0; otherwise,
  • ​0​, and the resulting view is empty.
2) The name views::stride denotes a RangeAdaptorObject. Given subexpressions e and n, the expression views::stride(e, n) is expression-equivalent to stride_view(e, n).
The n must be greater than ​0​, otherwise the behavior is undefined.

stride_view always models input_range, and models forward_range, bidirectional_range, random_access_range, and/or sized_range, if adapted view type V models the corresponding concept. stride_view<V> models common_range whenever the underlying view V does.

Contents

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 stride_view hold only two non-static data members:

  • the underlying view of type V (shown here as base_ for exposition only),
  • the size object (the "stride") of type ranges::range_difference_t<V> (shown here as stride_ for exposition only).

Member functions

 constructs a stride_view
(public member function) [edit]
(C++23)
 returns the stored stride value
(public member function)
returns a copy of the underlying (adapted) view
(public member function) [edit]
returns an iterator to the beginning
(public member function) [edit]
returns an iterator or a sentinel to the end
(public member function) [edit]
returns the number of elements. Provided only if the underlying (adapted) range satisfies sized_range.
(public member function) [edit]
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>) [edit]
(C++23)
 returns a constant iterator to the beginning of the range.
(public member function of std::ranges::view_interface<D>) [edit]
(C++23)
 returns a sentinel for the constant iterator of the 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]
returns the first element in the derived view. Provided if it satisfies forward_range.
(public member function of std::ranges::view_interface<D>) [edit]
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]

Deduction guides

Nested classes

(C++23)
 the iterator type
(exposition-only member class template*)

Helper templates

template< class V >

    inline constexpr bool ranges::enable_borrowed_range<stride_view<V>> =

        ranges::enable_borrowed_range<V>;
 (since C++23)

This specialization of ranges::enable_borrowed_range makes stride_view satisfy borrowed_range when the underlying view satisfies it.

Notes

Feature-test macro Value Std Feature
__cpp_lib_ranges_stride 202207L (C++23) std::ranges::stride_view

Example

A link to test: Compiler Explorer.

Run this code
#include <algorithm>
#include <iostream>
#include <ranges>
#include <string_view>
using namespace std::literals;
 
void print(std::ranges::viewable_range auto &&v, std::string_view separator = " ")
{
    for (auto const &x : v)
        std::cout << x << separator;
    std::cout << '\n';
}
 
int main()
{
    print(std::views::iota(1, 13) | std::views::stride(3));
    print(std::views::iota(1, 13) | std::views::stride(3) | std::views::reverse);
    print(std::views::iota(1, 13) | std::views::reverse | std::views::stride(3));
 
    print("0x0!133713337*x//42/A$"sv | std::views::stride(0B11) |
          std::views::transform([](char O) -> char { return 0100 + O; }),
          "");
}

Output: 

1 4 7 10
10 7 4 1
12 9 6 3
password

References

  • C++23 standard (ISO/IEC 14882:2024):
  • 26.7.30 Slide view [range.stride]

See also

(C++23)
 a view whose Mth element is a view over the Mth through (M + N - 1)th elements of another view
(class template) (range adaptor object)[edit]
(C++23)
 a range of views that are N-sized non-overlapping successive chunks of the elements of another view
(class template) (range adaptor object)[edit]
(C++23)
 a view consisting of tuples of references to adjacent elements of the adapted view
(class template) (range adaptor object)[edit]
(C++20)
 a view that consists of the elements of a range that satisfies a predicate
(class template) (range adaptor object)[edit]
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