[libcxx-commits] [PATCH] D128864: [libc++] Fix algorithms which use reverse_iterator

[Konstantin Varlamov via Phabricator via libcxx-commits]

var-const added inline comments.


================
Comment at: libcxx/include/__iterator/reverse_iterator.h:429
+  _LIBCPP_HIDE_FROM_ABI friend constexpr bool operator==(const _AlgRevIter& __lhs, const _AlgRevIter& __rhs) {
+    return __lhs.base() == __rhs.base();
+  }
----------------
philnik wrote:
> var-const wrote:
> > philnik wrote:
> > > var-const wrote:
> > > > Hmm, so this expression is not ambiguous, but when it's used as a constraint in a `requires` clause, it is considered ambiguous? Am I missing something?
> > > No, that's exactly the case.
> > Interesting. Why is that?
> I don't know exactly why, but I think it is because that would change the overload resolution. With the change in SFINAE contexts you could end up calling different functions, not just allow code that would otherwise be an error.
It looks like this paper aims to fix the language issue: https://github.com/cplusplus/papers/issues/1127
Unfortunately, even though the paper was approved this February, it doesn't fix all the potential cases that create ambiguity, so it won't change anything for us even after it's implemented in the compiler (or at least that's how I read it).


Repository:
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  https://reviews.llvm.org/D128864/new/

https://reviews.llvm.org/D128864