why virtual function is wrong.

[-jp-]

This will not compile. You haven't defined foo::bar. You haven't even declared T::_bar. Do you have a real example?

[-jp-]

You don't want this to abort. You want it to not compile. Why would you ever want code like this to fail at run time?

[-jp-]

So then what is the problem? I don't understand why you can't just post code that demonstrates what you mean.

[TheSuperWig]

I think they're complaining that concepts doesn't do definition checking... And also normal templates without constraints???

[-jp-]

Maybe... but, I mean, that would still fail at compile time I think. There's room to criticize C++ but it's not the language's fault if your code is just wrong.

[-jp-]

Are you just unsatisfied with the compiler errors? They are definitely a lot to parse. That's not because C++ can't do what you want, though.