On 15 May 2018 at 16:01, John McCall via cfe-dev <cfe-...@lists.llvm.org> wrote:
> On May 15, 2018, at 6:05 PM, George Karpenkov via cfe-dev < > cfe-...@lists.llvm.org> wrote: > > +cfe-dev > > Hi Andrea, > > I think you might get more luck asking on the cfe-dev mailing list. > > > George > > On May 15, 2018, at 1:15 PM, Andrea Arteaga via cfe-users < > cfe-users@lists.llvm.org> wrote: > > Dear all, > Recently, my team suffered from a bug due to a double bad usage of C++. > > We have a function returning a reference to an object: > > Object& GetObject(); > > Sometimes we use this function like this: > > auto obj = GetObject(); > > This triggers a copy of the object, which we really don't mean. The two > problems are: > 1. Object does not delete the copy constructor, nor does it declare one. > We have a policy of never using implicitly-declared constructors, we either > use `=delete` or `=default`. Nevertheless we missed this class. > > > Implicitly-defined copy constructors are ubiquitous in idiomatic C++. > Maybe that's not true in your project, but still, this seems too > special-case for the compiler. Maybe a linter that has a more > sophisticated model of what code is yours vs. the standard library. > > 2. A reference is demoted to a rvalue due to the usage of `auto` instead > of `auto&`. > > > This is a more reasonable thing to try to warn about. I have two concerns: > - I don't know a reasonable way to suppress the warning if you really do > want to load from the l-value. > - I have a non-specific worry that it'll disrupt some important idiom > that I'm just not thinking of. > How about: vector<some_complex_type> v = get_vector(); auto x = v.front(); or, worse: auto y = get_vector().front(); But those are concerns that we could explore during iterative design and > implementation. > > John. > > _______________________________________________ > cfe-dev mailing list > cfe-...@lists.llvm.org > http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev > >
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