[libcxx-commits] [libcxx] [libc++] Introduce `__product_iterator_traits` and optimise `flat_map::insert` (PR #139454)

[Louis Dionne via libcxx-commits]

================
@@ -251,6 +252,10 @@ class zip_view<_Views...>::__iterator : public __zip_view_iterator_category_base
 
   friend class zip_view<_Views...>;
 
+  using __is_zip_view_iterator _LIBCPP_NODEBUG = true_type;
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ldionne wrote:

```suggestion
  static constexpr bool __is_zip_view_iterator = true;
```

Slight simplification. This is what we do for `join_view::iterator` and segmented iterator traits.

https://github.com/llvm/llvm-project/pull/139454