std::ranges...r++,--,+=,-=(3)

💖 NAME 💖

okay so bestie, this is the std::ranges...r++,--,+=,-=(3) page from the C++ Standard Libary — yes, the header really says “Libary”, and honestly? iconic typo. 💅

The NAME says: std::ranges::adjacent_view::iterator::operator++,--,+=,-= - std::ranges::adjacent_view::iterator::operator++,--,+=,-= — yep, it says it twice, and we’re keeping both because rules are rules. ✨

This is the whole little family of iterator moves for adjacent_view’s iterator, and it’s giving C++23 from the very first line. 🦋

✨ Synopsis ✨

constexpr /*iterator*/& operator++();                   (1) (since C++23)
constexpr /*iterator*/ operator++( int );               (2) (since C++23)
constexpr /*iterator*/& operator--()                    (3) (since C++23)
    requires ranges::bidirectional_range<Base>;
constexpr /*iterator*/ operator--( int )                (4) (since C++23)
    requires ranges::bidirectional_range<Base>;
constexpr /*iterator*/& operator+=( difference_type n ) (5) (since C++23)
    requires ranges::random_access_range<Base>;
constexpr /*iterator*/& operator-=( difference_type n ) (6) (since C++23)
    requires ranges::random_access_range<Base>;

Increments or decrements the iterator. Let current_ be an underlying array of iterators. 💫

---

1) — Equivalent to:

for (auto& i : current_)
    i = std::ranges::next(i);
return *this;

⚠️ undefined behavior alert: the behavior is undefined if before the call current_.back() is not incrementable. Like, do not test fate, bestie. 💀

2) — Equivalent to:

auto tmp = *this;
++*this;
return tmp;

3) — Equivalent to:

for (auto& i : current_)
    i = std::ranges::prev(i);
return *this;

⚠️ undefined behavior alert: the behavior is undefined if before the call current_.front() is not decrementable. Again: not the vibe. 😭

4) — Equivalent to:

auto tmp = *this;
--*this;
return tmp;

5) — Equivalent to:

for (auto& i : current_)
    i = i + n;
return *this;

⚠️ undefined behavior alert: the behavior is undefined if before the call current_.back() + n does not have well-defined behavior. Read that twice, bestie. 💅

6) — Equivalent to:

for (auto& i : current_)
    i = i - n;
return *this;

⚠️ undefined behavior alert: the behavior is undefined if before the call current_.front() - n does not have well-defined behavior. periodt. 🔥

🌸 Parameters 🌸

• n — position relative to current location

🎀 Return value 🎀

• 1, 3, 5, 6) *this
• 2, 4) A copy of *this that was made before the change.

🧚 Example 🧚

// Run this code

#include <cassert>
#include <list>
#include <ranges>
#include <utility>
#include <vector>

[[nodiscard]]
bool operator==(std::pair<int&, int&> x, std::pair<int, int> y)
{
    return x.first == y.first and x.second == y.second;
}

int main()
{
    {
        auto v = std::vector{0, 1, 2, 3, 4, 5};
        auto i = (v | std::views::pairwise).begin();
        assert((*i == std::pair{0, 1}));
        ++i;                            // overload (1)
        assert((*i == std::pair{1, 2}));
        --i;                            // overload (3)
        assert((*i == std::pair{0, 1}));
        i += 2;                         // overload (5)
        assert((*i == std::pair{2, 3}));
        i -= 2;                         // overload (6)
        assert((*i == std::pair{0, 1}));
    }
    {
        auto v = std::list{0, 1, 2, 3, 4, 5};
        auto i = (v | std::views::pairwise).begin();
        assert((*i == std::pair{0, 1}));
        ++i;                            // overload (1)
        assert((*i == std::pair{1, 2}));
        --i;                            // overload (3)
        assert((*i == std::pair{0, 1}));
//      i += 2; // Error: v is not a random_access_range; overload (5)
//      i -= 2; // Error: v is not a random_access_range; overload (6)
    }
}

🔥 See also 🔥

• operator+ performs iterator arithmetic
• operator- (public member function)
• (C++23)

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okay that’s the whole page, bestie 🫶 — source: http://cppreference.com, version/date: 2024.06.10, manual: std::ranges...r++,--,+=,-=(3). go forth and increment responsibly. 💖✨