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.NET Forum / Languages / Managed C++ / March 2005ETI in VC71?
Hi all, I was under impression that the ETI bug was completely fixed in VC71. However, recently I ran into a problem that makes me think otherwise. The following minimal example demonstrates the problem that looks very similar to ETI: ------------------------------ template<int n> struct Y { typedef void type; }; template<> struct Y<4> {}; template<class T> T foo(); template <class T> struct X { typedef typename Y<sizeof(foo<T>())>::type type; }; int main() { return 0; } --------------------------------- Can anybody comment on this? Thanks in advance and best regards, Arkadiy > Hi all, > [quoted text clipped - 28 lines] > > Can anybody comment on this? AFIAK there were no significant changes in the way VC handles template instantiation in VC7.1 (or VC8). -cd > I was under impression that the ETI bug was completely fixed in VC71. > However, recently I ran into a problem that makes me think otherwise. > The following minimal example demonstrates the problem that looks very > similar to ETI: I think this a bit different from the nightmare in previous VC versions. [..] Specifically, I think VC doesn't realize that > template <class T> > struct X > { > typedef typename Y<sizeof(foo<T>())>::type type; is a dependent name. I can't access my VC 7.1 installation right now, but you could try to drop the typename and IIRC the compiler won't complain. Or try to add a "+ 0 * sizeof(T)" to make sure the compiler thinks it's a dependent name. So the compiler see typedef Y<4>::type type; in which case it's okay to instantiate Y<4>::type even if X<T>::type is not instantiated. So I think it's not exactly ETI. Nonetheless it's annoying enough. -hg > > I was under impression that the ETI bug was completely fixed in VC71. > > However, recently I ran into a problem that makes me think otherwise. [quoted text clipped - 15 lines] > compiler won't complain. Or try to add a "+ 0 * sizeof(T)" > to make sure the compiler thinks it's a dependent name. Second one helps. Now I have to figure out whether it solves my original problem or my minimal example was wrong. > So the compiler see typedef Y<4>::type type; > in which case it's okay to instantiate Y<4>::type even if > X<T>::type is not instantiated. > > So I think it's not exactly ETI. Nonetheless it's annoying > enough. Thanks a lot. Arkadiy > > I was under impression that the ETI bug was completely fixed in VC71. > > However, recently I ran into a problem that makes me think otherwise. [quoted text clipped - 15 lines] > compiler won't complain. Or try to add a "+ 0 * sizeof(T)" > to make sure the compiler thinks it's a dependent name. Second one helps. Now I have to figure out whether it solves my original problem or my minimal example was wrong. > So the compiler see typedef Y<4>::type type; > in which case it's okay to instantiate Y<4>::type even if > X<T>::type is not instantiated. > > So I think it's not exactly ETI. Nonetheless it's annoying > enough. Thanks a lot. Arkadiy > "Arkadiy" <vertleyb@hotmail.com> wrote > Specifically, I think VC doesn't realize that [quoted text clipped - 12 lines] > in which case it's okay to instantiate Y<4>::type even if > X<T>::type is not instantiated. As I mentioned before, adding "+ 0 * sizeof(T)" makes the code compile. However, if you take my original code and just replace 4 with any other number, it also compiles. If this was a problem of the compiler not recognizing a dependent name, the exact number used in the specialization wouldn't matter, would it? But, since 4 is exactly sizeof(int), this makes me to believe that the compiler tries to temporaruly replace "T" with integer, as in ETI. Regards, Arkadiy "Arkadiy" <vertleyb@hotmail.com> wrote in message >> Specifically, I think VC doesn't realize that >> [quoted text clipped - 19 lines] > sizeof(int), this makes me to believe that the compiler tries to > temporaruly replace "T" with integer, as in ETI. That depends on how you put it ;-) If you consider Y<sizeof(foo<T>())>::type a non-dependent name it should be interpreted. But, oc, T is not known at this point in time and probably substituted by an int. It's IMHO a bit different from the VC 6 ETI issues where it seemed that the compiler instantiated templates during parsing. Oc, both things might be symptoms of the same issue. BTW: The code compiles fine with VC 8 beta. -hg Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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