std::forward_iterator(3)

💅 std::forward_iterator — a page from the C++ Standard Libary manual, section 3

okay bestie, so this is the manual page for std::forward_iterator, straight out of the C++ Standard Libary manual (yes, section 3, she's official 👑). Sit down, get a lil snack 🍓, and let's get into it.

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✨ NAME ✨

std::forward_iterator — literally just std::forward_iterator, no notes 💀

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🦋 SYNOPSIS 🦋

So this concept lives in the header <iterator>, and here's exactly what she looks like:

template< class I >
concept forward_iterator =
    std::input_iterator<I> &&
    std::derived_from</*ITER_CONCEPT*/<I>, std::forward_iterator_tag> &&
    std::incrementable<I> &&
    std::sentinel_for<I, I>;

(since C++20) — she's a modern girlie, no cap ✨

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🌸 DESCRIPTION 🌸

The way this concept just refines std::input_iterator… obsessed. Here's the tea:

• she requires that I also models std::incrementable — which lowkey makes her suitable for multi-pass algorithms 🔥
• and she guarantees that two iterators to the same range can be compared against each other 🫶

Like, that's it, that's the whole vibe. Iconic behaviour, truly. 👑

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💜 NOTES 💜

okay this part matters, pay attention bestie 🙈 — unlike the LegacyForwardIterator requirements, the forward_iterator concept does not require dereference to return a reference. Not me being surprised by that… 😭 but fr fr, that's the actual rule.

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🧚 EXAMPLE 🧚

here's a minimum forward iterator, and honestly she ate:

#include <cstddef>
#include <iterator>

struct SimpleForwardIterator
{
    using difference_type = std::ptrdiff_t;
    using value_type = int;

    int operator*() const;

    SimpleForwardIterator& operator++();

    SimpleForwardIterator operator++(int)
    {
        auto tmp = *this;
        ++*this;
        return tmp;
    }

    bool operator==(const SimpleForwardIterator&) const;
};

static_assert(std::forward_iterator<SimpleForwardIterator>);

the static_assert at the end? that's the vibe check, and she passed 💅✨

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🌈 SEE ALSO 🌈

• input_iterator (C++20) — specifies that a type is an input iterator, that is, its referenced values can be read and it can be both pre- and post-incremented (concept)
• bidirectional_iterator (C++20) — specifies that a forward_iterator is a bidirectional iterator, supporting movement backwards (concept)

iykyk, the iterator family tree is giving main character energy 👑

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anyway that's the page!! source is http://cppreference.com, version 2024.06.10, and the date on the cover is 2024.06.10 too (she's stamped and dated, periodt). go forth and iterate forward bestie 💖🎀🦋