std::ranges:: views:: lazy_split, std::ranges:: lazy_split_view

From cppreference.com
C++
Ranges library
Range adaptors
std::ranges::lazy_split_view
Defined in header <ranges>
template < ranges:: input_range V, ranges:: forward_range Pattern >

requires ranges:: view < V > &&
ranges:: view < Pattern > &&
std:: indirectly_comparable < ranges:: iterator_t < V > ,
ranges:: iterator_t < Pattern > ,
ranges:: equal_to > &&
( ranges:: forward_range < V > || /*tiny-range*/ < Pattern > )
class lazy_split_view

: public ranges:: view_interface < lazy_split_view < V, Pattern >>
(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 */

constexpr ranges:: view auto lazy_split ( R && r, Pattern && pattern ) ;
(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*/ =
ranges:: sized_range < R > &&
requires { /* is-statically-constexpr-sized */ < R > ; } &&

( std:: remove_reference_t < R > :: size ( ) <= 1 ) ;
(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:

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.

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* )

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> )

Nested classes

the iterator type
( exposition-only member class template* )
the iterator type of the inner range
( exposition-only member class template* )

Deduction guides

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.

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 } { ! }

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

See also

(C++20)
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 range s
(class template) (range adaptor object)
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