[libcxx-commits] [libcxx] WIP [libc++][ranges] Applied [[nodiscard]] to `elements_view` (PR #206589)

[Lucas Mellone via libcxx-commits]

https://github.com/lknknm updated https://github.com/llvm/llvm-project/pull/206589

>From fde2218d5a8d799e9c2806a51ddd9758c2efd13e Mon Sep 17 00:00:00 2001
From: Lucas Mellone <github.snugness349 at passinbox.com>
Date: Mon, 29 Jun 2026 23:30:56 +0200
Subject: [PATCH 1/2] add: nodiscard to elements_view

---
 libcxx/include/__ranges/elements_view.h | 40 ++++++++++++-------------
 1 file changed, 20 insertions(+), 20 deletions(-)

diff --git a/libcxx/include/__ranges/elements_view.h b/libcxx/include/__ranges/elements_view.h
index b1419f2a1dd91..fc8c46b29b57f 100644
--- a/libcxx/include/__ranges/elements_view.h
+++ b/libcxx/include/__ranges/elements_view.h
@@ -77,57 +77,57 @@ class elements_view : public view_interface<elements_view<_View, _Np>> {
 
   _LIBCPP_HIDE_FROM_ABI constexpr explicit elements_view(_View __base) : __base_(std::move(__base)) {}
 
-  _LIBCPP_HIDE_FROM_ABI constexpr _View base() const&
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr _View base() const&
     requires copy_constructible<_View>
   {
     return __base_;
   }
 
-  _LIBCPP_HIDE_FROM_ABI constexpr _View base() && { return std::move(__base_); }
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr _View base() && { return std::move(__base_); }
 
-  _LIBCPP_HIDE_FROM_ABI constexpr auto begin()
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto begin()
     requires(!__simple_view<_View>)
   {
     return __iterator</*_Const=*/false>(ranges::begin(__base_));
   }
 
-  _LIBCPP_HIDE_FROM_ABI constexpr auto begin() const
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto begin() const
     requires range<const _View>
   {
     return __iterator</*_Const=*/true>(ranges::begin(__base_));
   }
 
-  _LIBCPP_HIDE_FROM_ABI constexpr auto end()
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto end()
     requires(!__simple_view<_View> && !common_range<_View>)
   {
     return __sentinel</*_Const=*/false>{ranges::end(__base_)};
   }
 
-  _LIBCPP_HIDE_FROM_ABI constexpr auto end()
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto end()
     requires(!__simple_view<_View> && common_range<_View>)
   {
     return __iterator</*_Const=*/false>{ranges::end(__base_)};
   }
 
-  _LIBCPP_HIDE_FROM_ABI constexpr auto end() const
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto end() const
     requires range<const _View>
   {
     return __sentinel</*_Const=*/true>{ranges::end(__base_)};
   }
 
-  _LIBCPP_HIDE_FROM_ABI constexpr auto end() const
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto end() const
     requires common_range<const _View>
   {
     return __iterator</*_Const=*/true>{ranges::end(__base_)};
   }
 
-  _LIBCPP_HIDE_FROM_ABI constexpr auto size()
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto size()
     requires sized_range<_View>
   {
     return ranges::size(__base_);
   }
 
-  _LIBCPP_HIDE_FROM_ABI constexpr auto size() const
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto size() const
     requires sized_range<const _View>
   {
     return ranges::size(__base_);
@@ -211,11 +211,11 @@ class elements_view<_View, _Np>::__iterator
     requires _Const && convertible_to<iterator_t<_View>, iterator_t<_Base>>
       : __current_(std::move(__i.__current_)) {}
 
-  _LIBCPP_HIDE_FROM_ABI constexpr const iterator_t<_Base>& base() const& noexcept { return __current_; }
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr const iterator_t<_Base>& base() const& noexcept { return __current_; }
 
-  _LIBCPP_HIDE_FROM_ABI constexpr iterator_t<_Base> base() && { return std::move(__current_); }
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr iterator_t<_Base> base() && { return std::move(__current_); }
 
-  _LIBCPP_HIDE_FROM_ABI constexpr decltype(auto) operator*() const { return __get_element(__current_); }
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr decltype(auto) operator*() const { return __get_element(__current_); }
 
   _LIBCPP_HIDE_FROM_ABI constexpr __iterator& operator++() {
     ++__current_;
@@ -261,7 +261,7 @@ class elements_view<_View, _Np>::__iterator
     return *this;
   }
 
-  _LIBCPP_HIDE_FROM_ABI constexpr decltype(auto) operator[](difference_type __n) const
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr decltype(auto) operator[](difference_type __n) const
     requires random_access_range<_Base>
   {
     return __get_element(__current_ + __n);
@@ -303,25 +303,25 @@ class elements_view<_View, _Np>::__iterator
     return __x.__current_ <=> __y.__current_;
   }
 
-  _LIBCPP_HIDE_FROM_ABI friend constexpr __iterator operator+(const __iterator& __x, difference_type __y)
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI friend constexpr __iterator operator+(const __iterator& __x, difference_type __y)
     requires random_access_range<_Base>
   {
     return __iterator{__x} += __y;
   }
 
-  _LIBCPP_HIDE_FROM_ABI friend constexpr __iterator operator+(difference_type __x, const __iterator& __y)
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI friend constexpr __iterator operator+(difference_type __x, const __iterator& __y)
     requires random_access_range<_Base>
   {
     return __y + __x;
   }
 
-  _LIBCPP_HIDE_FROM_ABI friend constexpr __iterator operator-(const __iterator& __x, difference_type __y)
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI friend constexpr __iterator operator-(const __iterator& __x, difference_type __y)
     requires random_access_range<_Base>
   {
     return __iterator{__x} -= __y;
   }
 
-  _LIBCPP_HIDE_FROM_ABI friend constexpr difference_type operator-(const __iterator& __x, const __iterator& __y)
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI friend constexpr difference_type operator-(const __iterator& __x, const __iterator& __y)
     requires sized_sentinel_for<iterator_t<_Base>, iterator_t<_Base>>
   {
     return __x.__current_ - __y.__current_;
@@ -365,14 +365,14 @@ class elements_view<_View, _Np>::__sentinel {
 
   template <bool _OtherConst>
     requires sized_sentinel_for<sentinel_t<_Base>, iterator_t<__maybe_const<_OtherConst, _View>>>
-  _LIBCPP_HIDE_FROM_ABI friend constexpr range_difference_t<__maybe_const<_OtherConst, _View>>
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI friend constexpr range_difference_t<__maybe_const<_OtherConst, _View>>
   operator-(const __iterator<_OtherConst>& __x, const __sentinel& __y) {
     return __get_current(__x) - __y.__end_;
   }
 
   template <bool _OtherConst>
     requires sized_sentinel_for<sentinel_t<_Base>, iterator_t<__maybe_const<_OtherConst, _View>>>
-  _LIBCPP_HIDE_FROM_ABI friend constexpr range_difference_t<__maybe_const<_OtherConst, _View>>
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI friend constexpr range_difference_t<__maybe_const<_OtherConst, _View>>
   operator-(const __sentinel& __x, const __iterator<_OtherConst>& __y) {
     return __x.__end_ - __get_current(__y);
   }

>From 4c961f7efb3efb1985259cd16b13fae3c23ef871 Mon Sep 17 00:00:00 2001
From: Lucas Mellone <github.snugness349 at passinbox.com>
Date: Mon, 29 Jun 2026 23:36:42 +0200
Subject: [PATCH 2/2] fix: clang format

---
 libcxx/include/__ranges/elements_view.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/libcxx/include/__ranges/elements_view.h b/libcxx/include/__ranges/elements_view.h
index fc8c46b29b57f..33c152bbd03b4 100644
--- a/libcxx/include/__ranges/elements_view.h
+++ b/libcxx/include/__ranges/elements_view.h
@@ -321,7 +321,8 @@ class elements_view<_View, _Np>::__iterator
     return __iterator{__x} -= __y;
   }
 
-  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI friend constexpr difference_type operator-(const __iterator& __x, const __iterator& __y)
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI friend constexpr difference_type
+  operator-(const __iterator& __x, const __iterator& __y)
     requires sized_sentinel_for<iterator_t<_Base>, iterator_t<_Base>>
   {
     return __x.__current_ - __y.__current_;