Difference between revisions of "cpp/ranges/chunk by view"

Revision as of 01:54, 12 February 2023

chunk_by_view always models forward_range, and models bidirectional_range and/or common_range, if adapted view type models the corresponding concepts. chunk_by_view never models borrowed_range or sized_range.

Expression-equivalent

Expression e is expression-equivalent to expression f, if

• e and f have the same effects, and
• either both are constant subexpressions or else neither is a constant subexpression, and
• either both are potentially-throwing or else neither is potentially-throwing (i.e. noexcept(e) == noexcept(f)).

Data members

Typical implementations of chunk_by_view hold three non-static data members:

• the underlying view of type V (shown here as base_ for exposition only),
• a wrapper that wraps the predicate used to split the elements of base_ of type movable-box<Pred> (shown here as pred_ for exposition only), where movable-box is a wrapper class template that always satisfies movable,
• an object of std::optional-like type (shown here as begin_ for exposition only) that caches an iterator to the first element.

Member functions

Deduction guides

Nested classes

Notes

In order to provide the amortized constant time complexity required by the range concept, the result of begin is cached within the chunk_by_view object. If the underlying range is modified after the first call to begin(), subsequent uses of the chunk_by_view object might have unintuitive behavior.

Example

#include <functional>
#include <iostream>
#include <ranges>
#include <string_view>
#include <vector>
 
void print_chunks(auto view, std::string_view separator = " ")
{
    for (auto const subrange : view)
    {
        std::cout << "[";
        for (std::string_view prefix = ""; auto const &elem : subrange)
        {
            std::cout << prefix << elem;
            prefix = separator;
        }
        std::cout << "] ";
    }
    std::cout << '\n';
}
 
int main()
{
    {
        auto v = std::vector{1, 2, 3, 1, 2, 3, 3, 3, 1, 2, 3};
        auto fun = std::ranges::less{};
        auto view = v | std::views::chunk_by(fun);
        print_chunks(view);
    }
    {
        auto v = std::vector{1, 2, 3, 4, 4, 0, 2, 3, 3, 3, 2, 1};
        auto fun = std::not_fn(std::ranges::equal_to{}); // or ranges::not_equal_to
        auto view = v | std::views::chunk_by(fun);
        print_chunks(view);
    }
    {
        std::string v = "__cpp_lib_ranges_chunk_by";
        auto fun = [](char x, char y) { return not(x == '_' or y == '_'); };
        auto view = v | std::views::chunk_by(fun);
        print_chunks(view, "");
    }
}

[1 2 3] [1 2 3] [3] [3] [1 2 3]
[1 2 3 4] [4 0 2 3] [3] [3 2 1]
[_] [_] [cpp] [_] [lib] [_] [ranges] [_] [chunk] [_] [by]

References

See also