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

template< ranges::input_range V, ranges::forward_range Pattern >
requires ranges::view<V> and
         ranges::view<Pattern> and
         std::indirectly_comparable<ranges::iterator_t<V>,
                                    ranges::iterator_t<Pattern>,
                                    ranges::equal_to> and
         (ranges::forward_range<V> or /* tiny-range */<Pattern>)
class lazy_split_view :
    public ranges::view_interface<lazy_split_view<V, Pattern>>

namespace views {
    inline constexpr /* unspecified */ lazy_split = /* unspecified */;
}

template< ranges::viewable_range R, class Pattern >
    requires /* see below */
constexpr ranges::view auto lazy_split( R&& r, Pattern&& pattern );

template< class Pattern >
constexpr /* range adaptor closure */ lazy_split( Pattern&& pattern );

template< class R >
concept /* tiny-range */ =      // exposition only
  ranges::sized_range<R> and
    requires /* is-statically-constexpr-sized */<R> and
      (std::remove_reference_t<R>::size() <= 1);

Two major scenarios are supported:

• The view is an input_range, the delimiter is a single element (wrapped in a single_view).
• The view is a forward_range, the delimiter is a view of elements.

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

Typical implementations of lazy_split_view hold two or three non-static data members:

• the underlying view of type V (shown here as base_ for exposition only),
• the pattern (shown here as pattern_ for exposition only) that is used as a delimiter to split the underlying view, and
• the caching object (shown here as current_ for exposition only) of the std::optional-like exposition-only type /* non-propagating-cache */<ranges::iterator_t<V>>. The current_ caches the result of calls to begin(). Present only if V does not satisfy forward_range.

Member functions

Nested classes

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

#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);
}

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.

See also