std::experi...erator_tag,(3)

✨ NAME ✨

std::experimental::ranges::input_iterator_tag — the whole little tag family, bestie 💅 (the man page title gets cut off but trust, it's the iterator tags from the C++ Standard Library and they're all here)

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🌸 Synopsis 🌸

okay so first, the squad lineup — these three are the ones the synopsis shouts out:

std::experimental::ranges::forward_iterator_tag,
std::experimental::ranges::bidirectional_iterator_tag,
std::experimental::ranges::random_access_iterator_tag

and they're all defined in header <experimental/ranges/iterator> 🎀

here's the actual structs, verbatim, no edits, i promise:

struct input_iterator_tag {};
struct output_iterator_tag {};
struct forward_iterator_tag : public input_iterator_tag {};
struct bidirectional_iterator_tag : public forward_iterator_tag {};
struct random_access_iterator_tag : public bidirectional_iterator_tag {};

so what are these? they define the category of an iterator 🦋. each tag is an empty type, and each one corresponds to one of the five iterator categories:

• input_iterator_tag corresponds to InputIterator.
• forward_iterator_tag corresponds to ForwardIterator.
• bidirectional_iterator_tag corresponds to BidirectionalIterator.
• random_access_iterator_tag corresponds to RandomAccessIterator.
• output_iterator_tag corresponds to OutputIterator — no cap, it's not used and provided solely for backward compatiblity (yes that's how it's spelled in the source, leave her alone 😭).

lowkey the whole point: iterator category tags carry information that can be used to select the most efficient algorithms for the specific requirement set that is implied by the category. iconic behaviour honestly. BUT — and this is the plot twist — concept-based overloading is preferred ✨.

one more rule, and it's a big one 👑: for every InputIterator type I, ranges::iterator_category_t<I> must be defined to be an alias for the most specific category tag that describes the iterator's behavior. periodt.

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🎀 Example 🎀

This section is incomplete Reason: no example

💀 not the empty example section. it's giving "trust me bro". moving on.

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🌈 See also 🌈

• input_iterator_tag
• output_iterator_tag
• forward_iterator_tag
• bidirectional_iterator_tag (class)
• random_access_iterator_tag
• contiguous_iterator_tag (C++20)

…all of those are empty class types used to indicate iterator categories 🫶

and also:

• iterator_traits — compatibility traits class that collects an iterator's associated types (alias template) ⭐

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🍓 Category 🍓

• Todo no example 🙈

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ngl the vibe check here is: empty structs, huge consequences. don't sleep on them 💜

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later bestie!! this page came from http://cppreference.com, version 2024.06.10 — slay, go read more, ily 💖✨