[libcxx-commits] [PATCH] D74292: [libcxx] adds [concept.derived]

[Casey Carter via Phabricator via libcxx-commits]

CaseyCarter added inline comments.


================
Comment at: libcxx/include/concepts:155-158
+template<class Derived, class Base>
+concept derived_from =
+    is_base_of_v<Base, Derived> &&
+    is_convertible_v<const volatile Derived*, const volatile Base*>;
----------------
miscco wrote:
> As before, this needs _Uglification.
> 
> Also note that `is_base_of_v` directly goes back to `__is_base_of` and you have the chain
> 
> __is_base_of -> i_base_of -> is_base_of_v
> 
> (See https://github.com/miscco/llvm-project/blob/bc29069dc401572ba62f7dd692a3474c1ead76c9/libcxx/include/type_traits#L1417-L1425)
> 
> So throughput would be better it you would again specialize for `__clang__` and use `__Is_base_of` directly
`__is_base_of(Base, Derived)` is available in all versions of clang/GCC/MSVC that support concepts (https://godbolt.org/z/xfLGbF).

`__is_convertible_to(From, To)` is available in clang/MSVC versions that support concepts (https://godbolt.org/z/jQEEr5). clang also supports the name `__is_convertible`.


Repository:
  rCXX libc++

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D74292/new/

https://reviews.llvm.org/D74292