std::ranges...::operator[](3)

okay so we're diving into std::ranges...::operator[](3) from the C++ Standard Libary — and yes, that's the manual name, spelled exactly like that in the header, no cap 💅. This page is all about the default operator[] for views, and it's lowkey iconic.

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💖 NAME 💖

std::ranges::view_interface::operator[] — and because the manual said it twice, we're saying it twice: std::ranges::view_interface::operator[]. It's giving "redundant but make it fashion." 🎀

🌸 Synopsis 🌸

Here's the exact signature tea, verbatim with all its funky line breaks:

          template<ranges::random_access_range R = D>
          constexpr decltype(auto) operator[]( ranges::range_difference_t<R>
       (1) (since C++20)
          n );
          template<ranges::random_access_range R = const D>
          constexpr decltype(auto) operator[]( ranges::range_difference_t<R>
       (2) (since C++20)
          n ) const;

The default implementation of this operator[] member function obtains the element at the specified offset relative to the beginning iterator, and it does that by reusing the operator[] of the iterator type. Cute, very on brand. 🦋

1. Let derived be static_cast<D&>(*this). Equivalent to return ranges::begin(derived)[n];.
2. Same as (1), except that derived is static_cast<const D&>(*this).

🎀 Parameters 🎀

• n — position of the element to return. That's the whole parameter list, bestie. 💅

✨ Return value ✨

The element at offset n relative to the beginning iterator. Slay. 🫶

🔥 Notes 🔥

In C++20, no type derived from std::ranges::view_interface in the standard library provides their own operator[] member function. Not a single one. 💀

However, these following derived types cannot use the default implementations, because they never satisfy random_access_range:

• std::ranges::basic_istream_view
• std::ranges::filter_view
• std::ranges::join_view
• std::ranges::lazy_split_view
• std::ranges::split_view

The inherited operator[] member function is available for std::ranges::empty_view, but a call to it always results in undefined behavior.

🚨 undefined behavior alert: like, do not call it on std::ranges::empty_view. That's not a vibe check you want to fail. 😭

🌈 Example 🌈

This section is incomplete. Reason: no example. The audacity. 😭

No example yet, so we're all just out here vibing with the signatures. 🧚

⭐ Category ⭐

• Todo no example. Yes, that's the category. It's giving "we'll get to it." 🎀

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Source/version check: http://cppreference.com, dated 2024.06.10, and the page is std::ranges...::operator[](3). Bye bestie, go index responsibly! 💖✨