[llvm-branch-commits] [libcxx] [libc++][format][3/7] Improves std::format performance. (PR #101817)

[Louis Dionne via llvm-branch-commits]

================
@@ -58,23 +59,156 @@ namespace __format {
 /// This helper is used together with the @ref back_insert_iterator to offer
 /// type-erasure for the formatting functions. This reduces the number to
 /// template instantiations.
+///
+/// The design of the class is being changed to improve performance and do some
+/// code cleanups.
+/// The original design (as shipped up to LLVM-19) uses the following design:
+/// - There is an external object that connects the buffer to the output.
+/// - The class constructor stores a function pointer to a grow function and a
+///   type-erased pointer to the object that does the grow.
----------------
ldionne wrote:

```suggestion
/// - The class constructor stores a function pointer to a "grow" function and a
///   type-erased pointer to the object that should be grown.
```

https://github.com/llvm/llvm-project/pull/101817