On Dec 30, 2015 11:53 AM, "Aaron Ballman" <aaron.ball...@gmail.com> wrote: > > On Wed, Dec 30, 2015 at 12:30 PM, Richard Smith <rich...@metafoo.co.uk> wrote: > > On Dec 30, 2015 6:34 AM, "Aaron Ballman" <aaron.ball...@gmail.com> wrote: > >> > >> aaron.ballman closed this revision. > >> aaron.ballman added a comment. > >> > >> Thanks! I've commit in r256643. > >> > >> > >> ================ > >> Comment at: test/SemaCXX/warn-literal-conversion.cpp:49-50 > >> @@ +48,4 @@ > >> + // values. > >> + bool b3 = 0.0f; > >> + bool b4 = 0.0; > >> +} > >> ---------------- > >> rsmith wrote: > >> > What about > >> > > >> > bool b5 = 1.0; > >> > bool b6 = 2.0; > >> > > >> > ? Arguably any `float` -> `bool` conversion changes the value (because > >> > `true` and `false` are not values of type `float`), so it wouldn't be > >> > completely unreasonable to warn even if the literal is `0.0`. > >> Except those conversions won't cause confusion to the user, so I'm not > >> certain what we gain by diagnosing. Given that some mental models expect > >> 0.99 to convert to 0, which converts to false (because bool is an integral > >> type, so it "must" do the usual integral truncation dance), it makes sense > >> to tell the user "no no no, that converts to true." I'm less convinced about > >> the utility of warning on things like `bool b = 1.99f' where it changes the > >> value from 1.99 to true. Perhaps this should be changed to only diagnose > >> when converting through an integer would result in a different value that > >> converting through the float? > > > > Let me ask a slightly different question: when would it ever be reasonable > > and intentional to initialize a bool from a floating-point *literal*? For > > integers, people use things like > > > > int n = 1e6; > > > > which is why we don't complain if the literal is exactly representable in > > the integer type. I can't imagine any similar cases for bool. > > I see what you're getting at now, and I agree that it wouldn't be > particularly reasonable. However, I think that there are two things to > warn about: initializing from a literal in general, and initializing > from a literal where the resulting Boolean value may be surprising. > While we're at it: is there ever a time where it's reasonable to > initialize a bool from a literal of type other than an integer or > bool? For instance: > > bool b1 = L'1'; > bool b2 = '1'; > bool b3 = 1.0f; > bool b4 = nullptr; // -Wnull-conversion catches this > > I think it makes sense for all of these to diagnose under > -Wliteral-conversion, but drop the "changes value" clause. > > bool b5 = 0.01; > bool b6 = '0'; > bool b7 = L'0'; > > I think it makes sense for these to diagnose under > -Wliteral-conversion, but with the changes value clause.
That makes sense to me. IIRC, we have seen initialization of a bool from a string literal "true" or -- worse -- "false" a few times. > ~Aaron > > > > >> > >> http://reviews.llvm.org/D15814 > >> > >> > >>
_______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
