OK.
On Fri, Aug 5, 2016 at 5:08 AM, Jonathan Wakely <jwak...@redhat.com> wrote: > On 27/07/16 18:06 -0400, Jason Merrill wrote: >> >> On Wed, Jul 27, 2016 at 8:05 AM, Jonathan Wakely <jwak...@redhat.com> >> wrote: >>> >>> Consider: >>> >>> template<typename T> T declval(); >>> >>> int& r1 = declval<int&&>(); >>> int&& r2 = declval<int&>(); >>> int& r3 = declval<const int&>(); >>> >>> >>> This produces three quite different errors: >>> >>> >>> refs.cc:3:25: error: invalid initialization of non-const reference of >>> type >>> 'int&' from an rvalue of type 'int' >>> int& r1 = declval<int&&>(); >>> ~~~~~~~~~~~~~~^~ >>> refs.cc:4:25: error: cannot bind 'int' lvalue to 'int&&' >>> int&& r2 = declval<int&>(); >>> ~~~~~~~~~~~~~^~ >>> refs.cc:5:30: error: binding 'const int' to reference of type 'int&' >>> discards qualifiers >>> int& r3 = declval<const int&>(); >>> ~~~~~~~~~~~~~~~~~~~^~ >>> >>> >>> The first one uses the order to/from, but the other two are from/to. >>> >>> The first and second are saying the same thing (wrong value category) >>> but very differently. >>> >>> The first and third mention references but the second doesn't. >>> >>> The standard talks about binding a reference to something, but the >>> second and third diagnostics talk about binding something to a >>> reference (and the first doesn't mention binding at all). >>> >>> The first diagnostic is specific to lvalue references (it wouldn't be >>> invalid if it was binding a non-const _rvalue_ reference to an >>> rvalue), but doesn't use the word "lvalue". >>> >>> (FWIW Clang and EDG both have their own inconsistencies for the same >>> example, but that shouldn't stop us trying to improve.) >>> >>> >>> IMHO the first should use the words "bind" and "lvalue reference": >>> >>> refs.cc:3:25: error: cannot bind non-const lvalue reference of type >>> 'int&' >>> to an rvalue of type 'int' >>> int& r1 = declval<int&&>(); >>> ~~~~~~~~~~~~~~^~ >>> >>> The second should use the phrasing "bind ref to value" instead of >>> "bind value to ref", and mention "rvalue reference": >>> >>> refs.cc:4:25: error: cannot bind rvalue reference of type 'int&&' to an >>> lvalue of type 'int' >>> int&& r2 = declval<int&>(); >>> ~~~~~~~~~~~~~^~ >>> >>> The third should use the same phrasing (but doesn't need to mention >>> lvalue/rvalue because the problem is related to cv-qualifiers not >>> value categories): >>> >>> refs.cc:5:30: error: binding reference of type 'int&' to 'const int' >>> discards qualifiers >>> int& r3 = declval<const int&>(); >>> ~~~~~~~~~~~~~~~~~~~^~ >>> >>> >>> I've only considered trivial examples here, is there some reason to >>> prefer to current diagnostics for more complex cases? >>> >>> The attached patch makes that change, but there are probably lots of >>> tests that would need updating which I haven't done until I know if >>> the change is worthwhile. >> >> >> Sounds good to me. > > > Here's the full patch then. There weren't too many tests to adjust. > > Tested x86_64-linux. OK for trunk? > >
