[cfe-dev] Templated operator overloading

[Nikola Smiljanic]

This sounds like http://llvm.org/bugs/show_bug.cgi?id=12961 to me. But it's
not clear if this is expected or not.


On Thu, May 22, 2014 at 6:12 PM, <antoni at buszta.info> wrote:

> Hi all,
>
> I have some small problem with clang behavior in such code:
>
> struct stream
> {
>     stream() {}
>     template<typename T>
>     inline stream& operator<<(T& t)
>     {
>         return *this;
>     }
> };
>
> template<typename Stream>
> inline Stream& operator<<(Stream& stream, int& t)
> {
>     return stream;
> }
>
> int main(int argc, char *argv[])
> {
>     int i = 42;
>     stream a;
>     a << i;
>
>     return 0;
> }
>
> This code compiles fine under clang (I have checked with 3.4 and current
> trunk) and gcc. However when I add -std=c++11 it still compiles fine under
> gcc but it stops compiling under clang. Error is:
>
> /home/abuszta/Development/llvm/bin/clang++ -std=c++11    operator.cpp
> -o operator
> operator.cpp:21:7: error: use of overloaded operator '<<' is ambiguous
> (with operand types 'stream' and 'int')
>     a << i;
>     ~ ^  ~
> operator.cpp:5:20: note: candidate function [with T = int]
>     inline stream& operator<<(T& t)
>                    ^
> operator.cpp:12:16: note: candidate function [with Stream = stream]
> inline Stream& operator<<(Stream& stream, int& t)
>                ^
> 1 error generated.
>
> In order to answer the question which behavior is good and which is bad I
> tried to find appropriate section in C++ standard. After analyzing 14.5.6.2
> (section about Partial ordering of function templates in N3337) and related
> I think there should not be any ambiguity after substitution and function
> should be choosed...
>
> What is more, when I make const stream a; this code compiles fine even
> with -std=c++11 and chooses the standalone function in favor to member
> function which suggests that there may be some problem with template
> resolution here.
>
> What is your interpretation of this behavior? Should I report bug?
>
> Best regards,
> Antoni Buszta.
> _______________________________________________
> cfe-dev mailing list
> cfe-dev at cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/cfe-dev/attachments/20140523/c7ea5b14/attachment.html>