[libcxx-commits] [libcxx] [libc++] Remove assumptions that std::array::iterator is a raw pointer (PR #74624)

[Louis Dionne via libcxx-commits]

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@@ -110,26 +111,32 @@ _LIBCPP_HIDE_FROM_ABI auto __copy(basic_string_view<_CharT> __str, output_iterat
   }
 }
 
-template <__fmt_char_type _CharT, __fmt_char_type _OutCharT = _CharT>
-_LIBCPP_HIDE_FROM_ABI auto
-__copy(const _CharT* __first, const _CharT* __last, output_iterator<const _OutCharT&> auto __out_it)
+template <contiguous_iterator _Iterator,
+          __fmt_char_type _CharT    = typename iterator_traits<_Iterator>::value_type,
+          __fmt_char_type _OutCharT = _CharT>
+_LIBCPP_HIDE_FROM_ABI auto __copy(_Iterator __first, _Iterator __last, output_iterator<const _OutCharT&> auto __out_it)
     -> decltype(__out_it) {
   return __formatter::__copy(basic_string_view{__first, __last}, std::move(__out_it));
 }
 
-template <__fmt_char_type _CharT, __fmt_char_type _OutCharT = _CharT>
-_LIBCPP_HIDE_FROM_ABI auto __copy(const _CharT* __first, size_t __n, output_iterator<const _OutCharT&> auto __out_it)
+template <contiguous_iterator _Iterator,
+          __fmt_char_type _CharT    = typename iterator_traits<_Iterator>::value_type,
+          __fmt_char_type _OutCharT = _CharT>
+_LIBCPP_HIDE_FROM_ABI auto __copy(_Iterator __first, size_t __n, output_iterator<const _OutCharT&> auto __out_it)
     -> decltype(__out_it) {
-  return __formatter::__copy(basic_string_view{__first, __n}, std::move(__out_it));
+  return __formatter::__copy(basic_string_view{std::to_address(__first), __n}, std::move(__out_it));
 }
 
 /// Transform wrapper.
 ///
 /// This uses a "mass output function" of __format::__output_buffer when possible.
-template <__fmt_char_type _CharT, __fmt_char_type _OutCharT = _CharT, class _UnaryOperation>
+template <contiguous_iterator _Iterator,
+          __fmt_char_type _CharT    = typename iterator_traits<_Iterator>::value_type,
+          __fmt_char_type _OutCharT = _CharT,
+          class _UnaryOperation>
 _LIBCPP_HIDE_FROM_ABI auto
-__transform(const _CharT* __first,
-            const _CharT* __last,
+__transform(_Iterator __first,
----------------
ldionne wrote:

> Is there a way we can do an OOB check ahead of time?

I think that might be possible, but I would approach it from the top down. So I would write this code in a generic fashion, and then I would ensure that it ends up only being called with (optionally OOB-checked) raw pointers to reduce the number of instantiations.

Also, at the end of the day, we're not instantiating this function with more unique types before/after this patch. We're just allowing the single type it's instantiated with to go from `char*` to `array<char>::iterator` seamlessly. The only additional weight we're adding is the concept constrained signature but it should only be instantiated with one iterator type regardless.

https://github.com/llvm/llvm-project/pull/74624