Quuxplusone added inline comments.
================ Comment at: include/concepts:175 +template <class _Tp, class _Up> +_LIBCPP_CONCEPT_DECL Same = __same_impl<_Tp, _Up> && __same_impl<_Up, _Tp>; + ---------------- CaseyCarter wrote: > Quuxplusone wrote: > > Peanut gallery asks: From lines 166-171 it looks awfully like > > `__same_impl<_Tp, _Up>` is true if and only if `__same_impl<_Up, _Tp>` is > > true. So why bother instantiating both templates? > This is the library implementation of the ["`Same<T, U>` subsumes `Same<U, > T>`" requirement](http://eel.is/c++draft/concept.same#1). Ah, so this and tangentially line 280 are both about fiddling with "subsumption." Admittedly I don't know how the compiler side is implemented, but it seems too bad that the library has to do double the work (even at this leafy of a level) just to deal with subsumption, which AIUI is required in order to properly order competing template specializations (a situation that is(?) unlikely to come up in the average end-user's code). :/ Anyway, carry on. ================ Comment at: include/concepts:394 + CommonReference< + const remove_reference_t<_Tp>&, + const remove_reference_t<_Up>&> && ---------------- CaseyCarter wrote: > Quuxplusone wrote: > > I'm fairly confident that `const remove_reference_t<_Tp>&` is just `const > > _Tp&`. > Not when `_Tp` is a reference type: https://godbolt.org/g/Q2Hon8. Ah, right, because of the `const`. Never mind! https://reviews.llvm.org/D49120 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
