[libcxx-commits] [PATCH] D100429: [libc++][ranges] Add range.cmp: equal_to, not_equal_to, less, etc.

[Tim Song via Phabricator via libcxx-commits]

tcanens added inline comments.


================
Comment at: libcxx/include/functional:3244
+  [[nodiscard]] constexpr bool operator()(_Tp &&__t, _Up &&__u) const {
+    return !(_VSTD::forward<_Tp>(__t) == _VSTD::forward<_Up>(__u));
+  }
----------------
cjdb wrote:
> zoecarver wrote:
> > Quuxplusone wrote:
> > > @ldionne, apparently we're free to use either expression `x != y` or `!(x == y)` here (because the whole point of `concept equality_comparable_with` is that those two expressions are interchangeable). I have a moderate preference for `x != y`, for simplicity and consistency with the ordinary `std::not_equal_to` — "we mean not-equal so let's write not-equal." What's your take? (See also my next comment below.)
> > > 
> > > https://en.cppreference.com/w/cpp/utility/functional/ranges/not_equal_to
> > I don't really care which thing we do. As for this comment and the one below, I'd be interested to hear other's opinions as well. I'm happy to implement whatever the consensus is. 
> Per [[ http://eel.is/c++draft/range.cmp | range.cmp ]], `not_equal_to::operator()` has effects equivalent to `return !ranges::equal_to{}(std::forward<T>(t), std::forward<U>(u))`.
> 
> I'd actually prefer to see all of the implementations return the expressions in the standard wording, verbatim.
I've removed the claim on cppreference that this can be implemented with `!=`; the convertible-to-pointer corner case means that it can't - consider a case where `==` results in a built-in comparing pointers but `!=` doesn't; we attach no semantic requirements to the `!=` in such a case.




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  https://reviews.llvm.org/D100429/new/

https://reviews.llvm.org/D100429