Difference between revisions of "cpp/ranges/lazy split view"
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| − | {{cpp/ranges/view title | lazy_split}} | + | {{cpp/ranges/view title|lazy_split}} |
{{cpp/ranges/lazy_split_view/navbar}} | {{cpp/ranges/lazy_split_view/navbar}} | ||
{{dcl begin}} | {{dcl begin}} | ||
| − | {{dcl header | ranges}} | + | {{dcl header|ranges}} |
| − | {{dcl | num=1 | since=c++20 |1= | + | {{dcl|num=1|since=c++20|1= |
template< ranges::input_range V, ranges::forward_range Pattern > | template< ranges::input_range V, ranges::forward_range Pattern > | ||
| − | requires ranges::view<V> && ranges::view<Pattern> && | + | requires ranges::view<V> && |
| − | + | ranges::view<Pattern> && | |
| − | + | std::indirectly_comparable<ranges::iterator_t<V>, | |
| − | + | ranges::iterator_t<Pattern>, | |
| − | class lazy_split_view : public ranges::view_interface<lazy_split_view<V, Pattern>> | + | ranges::equal_to> && |
| + | (ranges::forward_range<V> {{!!}} /*tiny-range*/<Pattern>) | ||
| + | class lazy_split_view | ||
| + | : public ranges::view_interface<lazy_split_view<V, Pattern>> | ||
}} | }} | ||
| − | {{dcl | num=2 | since=c++20 |1= | + | {{dcl|num=2|since=c++20|1= |
namespace views { | namespace views { | ||
| − | inline constexpr /*unspecified*/ lazy_split = /*unspecified*/; | + | inline constexpr /* unspecified */ lazy_split = /* unspecified */; |
} | } | ||
| + | }} | ||
| + | {{dcl h|Call signature}} | ||
| + | {{dcl|since=c++20|1= | ||
| + | template< ranges::viewable_range R, class Pattern > | ||
| + | requires /* see below */ | ||
| + | constexpr ranges::view auto lazy_split( R&& r, Pattern&& pattern ); | ||
| + | }} | ||
| + | {{dcl|since=c++20|1= | ||
| + | template< class Pattern > | ||
| + | constexpr /* range adaptor closure */ lazy_split( Pattern&& pattern ); | ||
| + | }} | ||
| + | {{dcl h|Helper concepts}} | ||
| + | {{dcl|num=3|notes={{mark expos}}|1= | ||
| + | template< class R > | ||
| + | concept /*tiny-range*/ = | ||
| + | ranges::sized_range<R> && | ||
| + | requires { /* is-statically-constexpr-sized */<R>; } && | ||
| + | (std::remove_reference_t<R>::size() <= 1); | ||
}} | }} | ||
{{dcl end}} | {{dcl end}} | ||
| Line 22: | Line 43: | ||
<!----> | <!----> | ||
Two major scenarios are supported: | Two major scenarios are supported: | ||
| − | * The view is | + | * The view is an {{lconcept|input_range}}, the delimiter is a single element (wrapped in a {{rlpt|single_view}}). |
* The view is a {{lconcept|forward_range}}, the delimiter is a {{lconcept|view}} of elements. | * The view is a {{lconcept|forward_range}}, the delimiter is a {{lconcept|view}} of elements. | ||
| − | |||
| − | |||
| − | @2@ The expression {{c|views::lazy_split( | + | @2@ A {{named req|RangeAdaptorObject}}. The expression {{c|views::lazy_split(e, f)}} is [[cpp/language/expressions#Expression-equivalence|expression-equivalent]] to {{c|lazy_split_view(e, f)}}<!-- LWG 3524 -->. |
| + | |||
| + | @3@ The exposition-only concept {{c|/*tiny-range*/<Pattern>}} is satisfied if {{tt|Pattern}} satisfies {{lconcept|sized_range}}, {{c|Pattern::size()}} is a constant expression and suitable as a template non-type argument, and the value of {{c|Pattern::size()}} is less than or equal to {{tt|1}}.<!-- The standard uses `std::remove_reference_t<R>::size()`, but since `Pattern` is a `view`, it cannot be a reference. --> Notably, {{rlpt|empty_view}} and {{rlpt|single_view}} satisfy this concept. | ||
| + | |||
| + | {{tt|lazy_split_view}} models the concepts {{lconcept|forward_range}} and {{lconcept|input_range}} when the underlying {{lconcept|view}} {{tt|V}} models respective concepts, and models {{lconcept|common_range}} when {{tt|V}} models both {{lconcept|forward_range}} and {{lconcept|common_range}}. | ||
| + | |||
| + | The inner range ({{c/core|ranges::range_reference_t<lazy_split_view>}}) models the concepts {{lconcept|forward_range}} and {{lconcept|input_range}} when the underlying {{lconcept|view}} {{tt|V}} models respective concepts. It does not model {{lconcept|common_range}}, and cannot be used with algorithms that expect a {{lconcept|bidirectional_range}} or higher. | ||
| + | |||
| + | ===Data members=== | ||
| + | {{dsc begin}} | ||
| + | {{dsc hitem|Member name|Definition}} | ||
| + | {{dsc expos mem obj|base_|private=yes|The underlying {{lconcept|view}} of type {{tt|V}}.}} | ||
| + | {{dsc expos mem obj|pattern_|private=yes|The pattern that is used as a delimiter to split the underlying {{lconcept|view}}.}} | ||
| + | {{dsc expos mem obj|current_|private=yes|maybe=yes|An [[cpp/ranges#Non-propagating cache|''optional-like'']] caching object of type {{c/core|1=/*non-propagating-cache*/<ranges::iterator_t<V>>}}. Caches the result of calls to {{rltf|begin}}. Present only if {{tt|V}} does not satisfy {{lconcept|forward_range}}.}} | ||
| + | {{dsc end}} | ||
===Member functions=== | ===Member functions=== | ||
{{dsc begin}} | {{dsc begin}} | ||
| − | {{dsc inc | cpp/ranges/adaptor/dsc constructor | lazy_split_view }} | + | {{dsc inc|cpp/ranges/adaptor/dsc constructor|lazy_split_view}} |
| − | {{dsc inc | cpp/ranges/adaptor/dsc base | lazy_split_view }} | + | {{dsc inc|cpp/ranges/adaptor/dsc base|lazy_split_view}} |
| − | {{dsc inc | cpp/ranges/adaptor/dsc begin | lazy_split_view }} | + | {{dsc inc|cpp/ranges/adaptor/dsc begin|lazy_split_view}} |
| − | {{dsc inc | cpp/ranges/adaptor/dsc end | lazy_split_view }} | + | {{dsc inc|cpp/ranges/adaptor/dsc end|lazy_split_view}} |
| + | |||
| + | {{cpp/ranges/view_interface/inherit|embedded=yes|data=invalid|size=invalid|back=invalid|operator[]=invalid}} | ||
{{dsc end}} | {{dsc end}} | ||
===Nested classes=== | ===Nested classes=== | ||
{{dsc begin}} | {{dsc begin}} | ||
| − | {{dsc mem | + | {{dsc expos mem tclass|cpp/ranges/lazy_split_view/outer_iterator|the iterator type}} |
| − | {{dsc mem | + | {{dsc expos mem tclass|cpp/ranges/lazy_split_view/inner_iterator|the iterator type of the inner range}} |
{{dsc end}} | {{dsc end}} | ||
==={{rl|deduction guides|Deduction guides}}=== | ==={{rl|deduction guides|Deduction guides}}=== | ||
| + | |||
| + | ===Notes=== | ||
| + | The name {{tt|lazy_split_view}} is introduced by the post-C++20 defect report {{wg21|P2210R2}}. It has the same lazy mechanism as that of the old {{tt|split_view}} before change. | ||
===Example=== | ===Example=== | ||
| Line 52: | Line 90: | ||
#include <ranges> | #include <ranges> | ||
#include <string_view> | #include <string_view> | ||
| − | |||
| − | |||
| − | |||
| − | |||
auto print = [](auto const& view) | auto print = [](auto const& view) | ||
{ | { | ||
| − | // `view` is | + | // `view` is of std::views::lazy_split_view::__outer_iterator::value_type |
for (std::cout << "{ "; const auto element : view) | for (std::cout << "{ "; const auto element : view) | ||
| Line 68: | Line 102: | ||
int main() | int main() | ||
{ | { | ||
| − | constexpr static auto source = { 0, 1,0, 2,3,0, 4,5,6,0, 7,8,9 }; | + | constexpr static auto source = {0, 1, 0, 2, 3, 0, 4, 5, 6, 0, 7, 8, 9}; |
| − | constexpr int delimiter {0}; | + | constexpr int delimiter{0}; |
| − | constexpr std::ranges::lazy_split_view | + | constexpr std::ranges::lazy_split_view outer_view{source, delimiter}; |
| − | std::cout << "splits[" << std::ranges::distance( | + | std::cout << "splits[" << std::ranges::distance(outer_view) << "]: "; |
| − | for (auto const& | + | for (auto const& inner_view: outer_view) |
| − | print( | + | print(inner_view); |
| − | constexpr std::string_view hello { "Hello C++ 20 !" }; | + | constexpr std::string_view hello{"Hello C++ 20 !"}; |
std::cout << "\n" "substrings: "; | std::cout << "\n" "substrings: "; | ||
std::ranges::for_each(hello {{!}} std::views::lazy_split(' '), print); | std::ranges::for_each(hello {{!}} std::views::lazy_split(' '), print); | ||
| − | + | ||
| − | constexpr std::string_view text { "Hello-+-C++-+-20-+-!" }; | + | constexpr std::string_view text{"Hello-+-C++-+-20-+-!"}; |
| − | constexpr std::string_view delim { "-+-" }; | + | constexpr std::string_view delim{"-+-"}; |
std::cout << "\n" "substrings: "; | std::cout << "\n" "substrings: "; | ||
std::ranges::for_each(text {{!}} std::views::lazy_split(delim), print); | std::ranges::for_each(text {{!}} std::views::lazy_split(delim), print); | ||
} | } | ||
| − | | output= | + | |output= |
| − | splits[5]: { } { 1 } { 2 3 } { 4 5 6 } { 7 8 9 } | + | splits[5]: { } { 1 } { 2 3 } { 4 5 6 } { 7 8 9 } |
substrings: { H e l l o } { C + + } { 2 0 } { ! } | substrings: { H e l l o } { C + + } { 2 0 } { ! } | ||
substrings: { H e l l o } { C + + } { 2 0 } { ! } | substrings: { H e l l o } { C + + } { 2 0 } { ! } | ||
}} | }} | ||
| + | |||
| + | ===Defect reports=== | ||
| + | {{dr list begin}} | ||
| + | {{dr list item|paper=P2210R2|std=C++20|before=the old {{tt|split_view}} was too lazy to be easily used|after=moves its functionality to {{tt|lazy_split_view}}}} | ||
| + | {{dr list end}} | ||
===See also=== | ===See also=== | ||
{{dsc begin}} | {{dsc begin}} | ||
| − | {{dsc inc | cpp/ranges/dsc split_view}} | + | {{dsc inc|cpp/ranges/dsc split_view}} |
| − | {{dsc inc | cpp/ranges/dsc join_view}} | + | {{dsc inc|cpp/ranges/dsc join_view}} |
{{dsc end}} | {{dsc end}} | ||
| − | {{langlinks|es|ja|ru|zh}} | + | {{langlinks|de|es|ja|ru|zh}} |
Latest revision as of 21:58, 20 June 2024
| Defined in header <ranges>
|
||
| template< ranges::input_range V, ranges::forward_range Pattern > requires ranges::view<V> && |
(1) | (since C++20) |
| namespace views { inline constexpr /* unspecified */ lazy_split = /* unspecified */; |
(2) | (since C++20) |
| Call signature |
||
| template< ranges::viewable_range R, class Pattern > requires /* see below */ |
(since C++20) | |
| template< class Pattern > constexpr /* range adaptor closure */ lazy_split( Pattern&& pattern ); |
(since C++20) | |
| Helper concepts |
||
| template< class R > concept /*tiny-range*/ = |
(3) | (exposition only*) |
1)
lazy_split_view takes a view and a delimiter, and splits the view into subranges on the delimiter.
Two major scenarios are supported:
- The view is an
input_range, the delimiter is a single element (wrapped in asingle_view). - The view is a
forward_range, the delimiter is aviewof elements.
2) A RangeAdaptorObject. The expression views::lazy_split(e, f) is expression-equivalent to lazy_split_view(e, f).
3) The exposition-only concept /*tiny-range*/<Pattern> is satisfied if
Pattern satisfies sized_range, Pattern::size() is a constant expression and suitable as a template non-type argument, and the value of Pattern::size() is less than or equal to 1. Notably, empty_view and single_view satisfy this concept.lazy_split_view models the concepts forward_range and input_range when the underlying view V models respective concepts, and models common_range when V models both forward_range and common_range.
The inner range (ranges::range_reference_t<lazy_split_view>) models the concepts forward_range and input_range when the underlying view V models respective concepts. It does not model common_range, and cannot be used with algorithms that expect a bidirectional_range or higher.
Contents |
[edit] Data members
| Member name | Definition |
base_ (private)
|
The underlying view of type V.(exposition-only member object*) |
pattern_ (private)
|
The pattern that is used as a delimiter to split the underlying view.(exposition-only member object*) |
current_ (private) (conditionally present) |
An optional-like caching object of type /*non-propagating-cache*/<ranges::iterator_t<V>>. Caches the result of calls to begin(). Present only if V does not satisfy forward_range.(exposition-only member object*) |
[edit] Member functions
constructs a lazy_split_view (public member function) | |
| returns a copy of the underlying (adapted) 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) | |
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>)
| |
[edit] Nested classes
| the iterator type (exposition-only member class template*) | |
| the iterator type of the inner range (exposition-only member class template*) |
[edit] Deduction guides
[edit] Notes
The name lazy_split_view is introduced by the post-C++20 defect report P2210R2. It has the same lazy mechanism as that of the old split_view before change.
[edit] Example
Run this code
#include <algorithm> #include <iostream> #include <ranges> #include <string_view> auto print = [](auto const& view) { // `view` is of std::views::lazy_split_view::__outer_iterator::value_type for (std::cout << "{ "; const auto element : view) std::cout << element << ' '; std::cout << "} "; }; int main() { constexpr static auto source = {0, 1, 0, 2, 3, 0, 4, 5, 6, 0, 7, 8, 9}; constexpr int delimiter{0}; constexpr std::ranges::lazy_split_view outer_view{source, delimiter}; std::cout << "splits[" << std::ranges::distance(outer_view) << "]: "; for (auto const& inner_view: outer_view) print(inner_view); constexpr std::string_view hello{"Hello C++ 20 !"}; std::cout << "\n" "substrings: "; std::ranges::for_each(hello | std::views::lazy_split(' '), print); constexpr std::string_view text{"Hello-+-C++-+-20-+-!"}; constexpr std::string_view delim{"-+-"}; std::cout << "\n" "substrings: "; std::ranges::for_each(text | std::views::lazy_split(delim), print); }
Output:
splits[5]: { } { 1 } { 2 3 } { 4 5 6 } { 7 8 9 }
substrings: { H e l l o } { C + + } { 2 0 } { ! }
substrings: { H e l l o } { C + + } { 2 0 } { ! }[edit] Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| P2210R2 | C++20 | the old split_view was too lazy to be easily used
|
moves its functionality to lazy_split_view
|
[edit] See also
a view over the subranges obtained from splitting another view using a delimiter(class template) (range adaptor object) | |
| (C++20) |
a view consisting of the sequence obtained from flattening a view of ranges(class template) (range adaptor object) |
