[libcxx-commits] [PATCH] D140259: [libc++] Add __small_buffer

[Louis Dionne via Phabricator via libcxx-commits]

ldionne accepted this revision.
ldionne added inline comments.


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Comment at: libcxx/include/__utility/small_buffer.h:25-28
+// __small_buffer helper for type-erasing classes like move_only_function to store small objects in a local buffer.
+// Only objects that are trivially relocatable can be stored inside it to allow __small_buffer to be trivially
+// relocatable itself. Since the buffer doesn't know what's stored inside it, the user has to manage the object's
+// lifetime, in particular the destruction of the object.
----------------



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Comment at: libcxx/include/__utility/small_buffer.h:38-43
+  template <class _Tp>
+  static constexpr bool __fits_in_buffer = [] {
+    using _DTp = decay_t<_Tp>;
+    return is_trivially_move_constructible_v<_DTp> && is_trivially_destructible_v<_DTp> &&
+           sizeof(_DTp) <= _BufferSize && alignof(_DTp) <= _BufferAlignment;
+  }();
----------------
This avoids instantiating a lambda and it's pretty easy to do, so we might as well.


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Comment at: libcxx/include/__utility/small_buffer.h:45-52
+  __small_buffer()                                 = default;
+  __small_buffer(const __small_buffer&)            = delete;
+  __small_buffer& operator=(const __small_buffer&) = delete;
+  ~__small_buffer()                                = default;
+
+  // Relocates the buffer - __delete() should never be called on a moved-from __small_buffer
+  __small_buffer(__small_buffer&&)            = default;
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I think the `= default` ones should be `_LIBCPP_HIDE_FROM_ABI`, since they *are* generated at the end of the day.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D140259/new/

https://reviews.llvm.org/D140259