std::end(std::valarray)(3)

okay so bestie, this is std::end(std::valarray)(3) from the C++ Standard Libary manual — yes, that spelling is literally in the header and we are not fixing it, we respect the iconique typo 💅. It's giving “tiny overload with big range-for energy,” and we’re gonna go through every single detail together. 🫶

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💖 NAME 💖

std::end(std::valarray) - literally std::end(std::valarray), no cap. That’s the whole name, bestie. ✨

✨ Synopsis ✨

template< class T >                          (1) (since C++11)
/* see below */ end( valarray<T>& v );
template< class T >                          (2) (since C++11)
/* see below */ end( const valarray<T>& v );

The overload of std::end for valarray returns an iterator of unspecified type referring to the one past the last element in the numeric array. So it’s the “end” iterator vibe, but the exact type is a mystery — unspecified, not our business, moving on. 💫

1. The return type must
   • meet the requirements of mutable LegacyRandomAccessIterator,
   • model contiguous_iterator, (since C++20)
   • have a member type value_type, which is T, and
   • have a member type reference, which is T&.
2. The return type must
   • meet the requirements of constant LegacyRandomAccessIterator,
   • model contiguous_iterator, (since C++20)
   • have a member type value_type, which is T, and
   • have a member type reference, which is const T&.

lowkey important, bestie: the iterator returned from this function is invalidated when the member function resize() is called on v or when the lifetime of v ends, whichever comes first. So don’t hold onto it like it’s a forever text, because it is not 😭.

🎀 Parameters 🎀

• v — a numeric array. That’s it. That’s the parameter. Slay. 🌸

🌸 Return value 🌸

Iterator to one past the last value in the numeric array. Classic end-of-range behavior, no notes. 💖

🦋 Exceptions 🦋

May throw implementation-defined exceptions. So like… ask your implementation, bestie. 🦋

💅 Notes 💅

Unlike other functions that take std::valarray arguments, end() cannot accept the replacement types (such as the types produced by expression templates) that may be returned from expressions involving valarrays: std::end(v1 + v2) is not portable, and std::end(std::valarray<T>(v1 + v2)) has to be used instead. So don’t try to be cute with std::end(v1 + v2) in portable code, because it’s giving not-portable vibes and we don’t do that. 🙈

The intent of this function is to allow range for loops to work with valarrays, not to provide container semantics. So it’s a range-for helper, not a whole container glow-up. Periodt. 💅

🌈 Example 🌈

Run this code, bestie:

// Run this code

#include <algorithm>
#include <iostream>
#include <valarray>

int main()
{
    const std::valarray<char> va
    {
        'H', 'e', 'l', 'l', 'o',
        ',', ' ',
        'C', '+', '+', '!', '\n'
    };

    std::for_each(std::begin(va), std::end(va),
                  [](char c){ std::cout << c; });
}

⭐ Output ⭐

Hello, C++!

🔥 Defect reports 🔥

The following behavior-changing defect reports were applied retroactively to previously published C++ standards. This is the “we fixed it after the fact” section, and it ate. 💅

• DR LWG 2058 — applied to C++11
  • 1. behavior as published: end() was required to support replacement types → correct behavior: 1. not required
  • 2. behavior as published: it was unspecified when the returned iterators will be invalidated → correct behavior: 2. specified

👑 See also 👑

• std::begin(std::valarray) — overloads std::begin (C++11) (function template)

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mwah 💋 — source: http://cppreference.com, version/date: 2024.06.10, page: std::end(std::valarray)(3). That’s the footer, bestie, and that’s the whole vibe. periodt. 🫶