> 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 <mailto: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. But those are concerns that we could explore during iterative design and implementation. John.
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