[libcxx-commits] [libcxx] [libc++] Introduce basic_string::__allocate_long_buffer_for_growing (PR #162633)

[Louis Dionne via libcxx-commits]

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@@ -2285,6 +2285,22 @@ private:
     return __long(__buffer, __capacity);
   }
 
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 __long
+  __allocate_long_buffer_for_growing(_Allocator& __alloc, size_type __required_capacity) {
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ldionne wrote:

I'd like to capture the fact that this growth pattern is intended specifically to prevent quadratic behavior when pushing back N elements into the string. As it stands, I find the name somewhat confusing since we almost always call `__allocate_long_buffer` for growing in some way, already.

If we have that, then I think that whether we perform the allocation in this function or outside it is not super important.

We should also add a comment explaining that it's the purpose of that function.

Maybe `__allocate_long_buffer_for_amortized_growth`? Or, at that point, just `__get_amortized_growth_capacity` and then allocate in the existing `__allocate_long_buffer`?

https://github.com/llvm/llvm-project/pull/162633