[libcxx-commits] [libcxx] [lldb] [libcxx] adds size-based `__split_buffer` representation to unstable ABI (PR #139632)

[Christopher Di Bella via libcxx-commits]

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@@ -45,13 +47,129 @@ _LIBCPP_PUSH_MACROS
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-// __split_buffer allocates a contiguous chunk of memory and stores objects in the range [__begin_, __end_).
-// It has uninitialized memory in the ranges  [__first_, __begin_) and [__end_, __cap_). That allows
-// it to grow both in the front and back without having to move the data.
+template <class _SplitBuffer, class _Tp, class _Allocator>
+class __split_buffer_pointer_layout {
+protected:
+  using value_type                     = _Tp;
+  using allocator_type                 = _Allocator;
+  using __alloc_rr _LIBCPP_NODEBUG     = __libcpp_remove_reference_t<allocator_type>;
+  using __alloc_traits _LIBCPP_NODEBUG = allocator_traits<__alloc_rr>;
+  using reference                      = value_type&;
+  using const_reference                = const value_type&;
+  using size_type                      = typename __alloc_traits::size_type;
+  using difference_type                = typename __alloc_traits::difference_type;
+  using pointer                        = typename __alloc_traits::pointer;
+  using const_pointer                  = typename __alloc_traits::const_pointer;
+  using iterator                       = pointer;
+  using const_iterator                 = const_pointer;
+
+public: // TODO: make private after vector becomes size-based
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cjdb wrote:

The primary reason for these to be public is because `vector::__swap_out_circular_buffer` needs to swap its data members with `__split_buffer`'s. I think I can get the next patch to end up refactoring this so that the equivalent `__vector_*_layout` classes can swap with `__split_buffer_*_layout` without breaking encapsulation.

https://github.com/llvm/llvm-project/pull/139632