[libcxx] [llvm] [clang-tools-extra] [clang] [libc++][span] P2821R5: span.at() (PR #74994)

[Mark de Wever via cfe-commits]

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@@ -343,6 +347,15 @@ public:
         return __data_[__idx];
     }
 
+#  if _LIBCPP_STD_VER >= 26
+    _LIBCPP_HIDE_FROM_ABI constexpr reference at(size_type __idx) const {
+      if (__idx >= size()) {
+        __throw_out_of_range();
+      }
+      return *(data() + __idx);
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mordante wrote:

And `std::__throw_out_of_range()` for consistency.

I prefer not to use `data()[__idx]`. This differs from the wording in the paper.

https://github.com/llvm/llvm-project/pull/74994