std::ranges::views::lazy_split, 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*/ =      // exposition only
  ranges::sized_range<R> &&
    requires /*is-statically-constexpr-sized*/<R> &&
      (std::remove_reference_t<R>::size() <= 1);
(3) (since C++20)
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 range adaptor object. 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

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

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>)
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


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.


#include <algorithm>
#include <iostream>
#include <ranges>
#include <string_view>
// P2210R2: a temporary patch until online g++ >= 12
#define lazy_split_view split_view
#define lazy_split split
auto print = [](auto const& view)
    // `view` is a 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)
    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.

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

a view over the subranges obtained from splitting another view using a delimiter
(class template) (range adaptor object)
a view consisting of the sequence obtained from flattening a view of ranges
(class template) (range adaptor object)

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