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

From cppreference.com
< cpp‎ | ranges
(+page, +example)
 
m (→‎Helper templates: -`inline`)
 
(9 intermediate revisions by 3 users not shown)
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template< ranges::input_range V >
 
template< ranges::input_range V >
 
     requires ranges::view<V>
 
     requires ranges::view<V>
−
class stride_view :
+
class stride_view
−
     public ranges::view_interface<stride_view<V>>
+
     : public ranges::view_interface<stride_view<V>>
 
}}
 
}}
 
{{dcl|num=2|since=c++23|1=
 
{{dcl|num=2|since=c++23|1=
Line 15: Line 15:
 
}}
 
}}
 
{{dcl h|Call signature}}
 
{{dcl h|Call signature}}
−
{{dcl|since=c++23|1=<!-- TODO: recheck -->
+
{{dcl|since=c++23|1=
 
template< ranges::viewable_range R >
 
template< ranges::viewable_range R >
−
constexpr ranges::view auto stride( R&& r, ranges::range_difference_t<V> n );
+
constexpr ranges::view auto stride( R&& r, ranges::range_difference_t<R> n );
 
}}
 
}}
−
{{dcl|since=c++23|1=<!-- TODO: recheck -->
+
{{dcl|since=c++23|1=
−
template< ranges::forward_range V >
+
template< class DifferenceType >
−
    requires ranges::view<V>
+
constexpr /*range adaptor closure*/ stride( DifferenceType&& n );
−
constexpr __range_adaptor_closure stride( ranges::range_difference_t<V> n );
+
 
}}
 
}}
 
{{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}}
  
−
@1@ {{tt|stride_view}} is a range adaptor that takes a {{lconcept|view}} and a number {{tt|''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 {{tt|''m''}}{{sup|th}} element of the produced view is {{tt|''(n * i)''}}{{sup|th}} element of the original view, for some non-negative index {{tt|''i''}}.
+
@1@ {{tt|stride_view}} is a range adaptor that takes a {{lconcept|view}} and a number {{tti|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 {{tti|m}}{{sup|''th''}} element of the produced view is {{tti|(n * i)}}{{sup|th}} element of the original view, for some non-negative index {{tti|i}}.
−
The elements of the original view, whose "index" is not a multiple of {{tt|''n''}}, are not present in the produced view.
+
The elements of the original view, whose "index" is not a multiple of {{tti|n}}, are not present in the produced view.
  
−
@@ Let {{tt|''S''}} be the size of the original view. Then the size of produced view is:
+
@@ Let {{tti|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.
  
−
@2@ The name {{c|views::stride}} denotes a {{named req|RangeAdaptorObject}}. Given subexpressions {{c|e}} and {{c|n}}, the expression {{c|views::stride(e, n)}} is ''expression-equivalent'' to {{c|stride_view(e, n)}}.
+
@2@ The name {{c|views::stride}} denotes a {{named req|RangeAdaptorObject}}. Given subexpressions {{c|e}} and {{c|n}}, the expression {{c|views::stride(e, n)}} is [[cpp/language/expressions#Expression-equivalence|expression-equivalent]] to {{c|stride_view(e, n)}}.
  
 
@@ The {{tt|n}} must be greater than {{c|0}}, otherwise the behavior is undefined.
 
@@ The {{tt|n}} must be greater than {{c|0}}, otherwise the behavior is undefined.
  
 
{{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}}
+
  
 
===Data members===
 
===Data members===
−
Typical implementations of {{tt|stride_view}} hold only two non-static data members:
+
{{dsc begin}}
−
* the underlying {{lconcept|view}} of type {{tt|V}} (shown here as {{tt|''base_''}} for exposition only),
+
{{dsc hitem|Member object|Definition}}
−
* the size object (the "stride") of type {{c|ranges::range_difference_t<V>}} (shown here as {{tt|''stride_''}} for exposition only).
+
{{dsc expos mem obj|base_|private=yes|The underlying {{lconcept|view}} of type {{tt|V}}.}}
 +
{{dsc expos mem obj|stride_|private=yes|The size object (the "stride") of type {{c|ranges::range_difference_t<V>}}.}}
 +
{{dsc end}}
  
 
===Member functions===
 
===Member functions===
 
{{dsc begin}}
 
{{dsc begin}}
 
{{dsc inc|cpp/ranges/adaptor/dsc constructor|stride_view}}
 
{{dsc inc|cpp/ranges/adaptor/dsc constructor|stride_view}}
−
{{dsc inc|cpp/ranges/stride_view/dsc stride}} <!-- TODO: "dsc stride" -->
+
{{dsc mem fun|cpp/ranges/stride_view/stride|returns the stored stride value|notes={{mark c++23}}}}
 
{{dsc inc|cpp/ranges/adaptor/dsc base|stride_view}}
 
{{dsc inc|cpp/ranges/adaptor/dsc base|stride_view}}
 
{{dsc inc|cpp/ranges/adaptor/dsc begin|stride_view}}
 
{{dsc inc|cpp/ranges/adaptor/dsc begin|stride_view}}
Line 71: Line 70:
 
{{ddcl|since=c++23|1=
 
{{ddcl|since=c++23|1=
 
template< class V >
 
template< class V >
−
    inline constexpr bool ranges::enable_borrowed_range<stride_view<V>> =
+
constexpr bool ranges::enable_borrowed_range<stride_view<V>> =
−
        ranges::enable_borrowed_range<V>;
+
    ranges::enable_borrowed_range<V>;
 
}}
 
}}
 
This specialization of {{ltt|cpp/ranges/borrowed_range|ranges::enable_borrowed_range}} makes {{tt|stride_view}} satisfy {{lconcept|borrowed_range}} when the underlying view satisfies it.
 
This specialization of {{ltt|cpp/ranges/borrowed_range|ranges::enable_borrowed_range}} makes {{tt|stride_view}} satisfy {{lconcept|borrowed_range}} when the underlying view satisfies it.
Line 81: Line 80:
 
===Example===
 
===Example===
 
{{example
 
{{example
−
|A link to test: [https://godbolt.org/z/z9e54WYT3 Compiler Explorer].
 
 
|code=
 
|code=
 
#include <algorithm>
 
#include <algorithm>
Line 89: Line 87:
 
using namespace std::literals;
 
using namespace std::literals;
  
−
void print(std::ranges::viewable_range auto &&v, std::string_view separator = " ")
+
void print(std::ranges::viewable_range auto&& v, std::string_view separator = " ")
 
{
 
{
−
     for (auto const &x : v)
+
     for (auto const& x : v)
 
         std::cout << x << separator;
 
         std::cout << x << separator;
 
     std::cout << '\n';
 
     std::cout << '\n';
Line 98: Line 96:
 
int main()
 
int main()
 
{
 
{
−
     print(std::views::iota(1, 11) {{!}} std::views::stride(3));
+
     print(std::views::iota(1, 13) {{!}} std::views::stride(3));
−
     print(std::views::iota(1, 11) {{!}} std::views::stride(3) {{!}} std::views::reverse);
+
     print(std::views::iota(1, 13) {{!}} std::views::stride(3) {{!}} std::views::reverse);
−
     print(std::views::iota(1, 11) {{!}} std::views::reverse {{!}} std::views::stride(3));
+
     print(std::views::iota(1, 13) {{!}} std::views::reverse {{!}} std::views::stride(3));
  
−
     print("0x0!133713337*x//42/A$"sv {{!}} std::views::stride(0B11) {{!}}
+
     print("0x0!133713337*x//42/A$@"sv {{!}} std::views::stride(0B11) {{!}}
−
           std::views::transform([](char O) -> char { return 0100 + O; }),
+
           std::views::transform([](char O) -> char { return 0100 {{!}} O; }),
 
           "");
 
           "");
 
}
 
}
Line 109: Line 107:
 
1 4 7 10
 
1 4 7 10
 
10 7 4 1
 
10 7 4 1
−
10 7 4 1
+
12 9 6 3
 
password
 
password
 
}}
 
}}
Line 115: Line 113:
 
===References===
 
===References===
 
{{ref std c++23}}
 
{{ref std c++23}}
−
{{ref std|title=Slide view|id=range.stride|section=26.7.30}}
+
{{ref std|title=Stride view|id=range.stride|section=26.7.31}}
 
{{ref std end}}
 
{{ref std end}}
  

Latest revision as of 18:57, 15 June 2024

 
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<R> n );
 (since C++23)
template< class DifferenceType >
constexpr /*range adaptor closure*/ stride( DifferenceType&& 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

[edit] Data members

Member object Definition
base_ (private) The underlying view of type V.
(exposition-only member object*)
stride_ (private) The size object (the "stride") of type ranges::range_difference_t<V>.
(exposition-only member object*)

[edit] 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]

[edit] Deduction guides

[edit] Nested classes

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

[edit] Helper templates

template< class V >

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.

[edit] Notes

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

[edit] Example

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

[edit] References

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

[edit] 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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