Difference between revisions of "cpp/ranges/lazy split view"

Revision as of 08:18, 20 January 2022

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

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>
 
// 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)
        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