C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Code question that involves namespaces, templates and classe          C++Talk.NET Forum Index -> C++ language (comp.lang.c++) View previous topic :: View next topic   Author Message Bernd Fuhrmann Guest Posted: Sat Dec 27, 2003 6:02 pm    Post subject: Code question that involves namespaces, templates and classe Hi! I just tried to write a little program, but GCC (Mingw 3.3.1) refused to compile it. So I'd like to know if there's something wrong with my code or if it is a bug in GCC. ---snip--- namespace Namespace {} template <class TSomeType> class TAlpha { public: int Namespace; }; template <class TSomeType> class TBeta : public TAlpha<TSomeType> { public: int method(int n) {Namespace=n;} }; int main() { } ---snip--- Gcc complains about using a namespace "Namespace" as expression, while it should in fact access TAlpha::Namespace. So, is it a bug in GCC or is my code simply wrong? TIA Bernd Fuhrmann Back to top Victor Bazarov Guest Posted: Sat Dec 27, 2003 6:39 pm    Post subject: Re: Code question that involves namespaces, templates and cl "Bernd Fuhrmann" <silverbanana (AT) gmx (DOT) de> wrote... Quote: I just tried to write a little program, but GCC (Mingw 3.3.1) refused to compile it. So I'd like to know if there's something wrong with my code or if it is a bug in GCC. ---snip--- namespace Namespace {} template class TAlpha { public: int Namespace; }; template class TBeta : public TAlpha { public: int method(int n) {Namespace=n;} Your 'int' function is also supposed to return something. Quote: }; int main() { } ---snip--- Gcc complains about using a namespace "Namespace" as expression, while it should in fact access TAlpha::Namespace. Should it? Why do you say that? And why don't you help it by fully qualifying the name you need? Quote: So, is it a bug in GCC or is my code simply wrong? Your code is simply wrong (as are your assumptions). Every name is looked up during the syntax check of the template (you don't have it instantiated, so no other check is done). In the expression in question, there is a name of a namespace on the left of the assignment operator. Victor Back to top Bernd Fuhrmann Guest Posted: Sat Dec 27, 2003 7:02 pm    Post subject: Re: Code question that involves namespaces, templates and cl Victor Bazarov wrote: Quote: Your 'int' function is also supposed to return something. ACK. Gcc complains about using a namespace "Namespace" as expression, while it should in fact access TAlpha::Namespace. Should it? Why do you say that? Because it doesn't seem wise to check names in a not (yet) used piece of code, while instantiation of it might change the accessed C++ constructs. Furthermore I think templates should not interfere in that way. Ok, I admit it's just a feeling of what C++ should be like, but I'm not yet totally convinced that my little piece of code is definately wrong. Quote: And why don't you help it by fully qualifying the name you need? Well I might, of course. But I didn't and I was wondering why it did not work and if that is justified. Quote: So, is it a bug in GCC or is my code simply wrong? Your code is simply wrong (as are your assumptions). Every name is looked up during the syntax check of the template (you don't have it instantiated, so no other check is done). In the expression in question, there is a name of a namespace on the left of the assignment operator. Obviously, yes. But how can the compiler know for sure that this name does refer to a namespace while instantiation might change that? Is that kind of name checking founded in ISO C++ or is it just the usual way to do things in a C++ compiler? TIA again, Bernd Fuhrmann Back to top Victor Bazarov Guest Posted: Sat Dec 27, 2003 9:23 pm    Post subject: Re: Code question that involves namespaces, templates and cl "Bernd Fuhrmann" <silverbanana (AT) gmx (DOT) de> wrote... Quote: Victor Bazarov wrote: Your 'int' function is also supposed to return something. ACK. Gcc complains about using a namespace "Namespace" as expression, while it should in fact access TAlpha::Namespace. Should it? Why do you say that? Because it doesn't seem wise to check names in a not (yet) used piece of code, while instantiation of it might change the accessed C++ constructs. Furthermore I think templates should not interfere in that way. Ok, I admit it's just a feeling of what C++ should be like, but I'm not yet totally convinced that my little piece of code is definately wrong. And why don't you help it by fully qualifying the name you need? Well I might, of course. But I didn't and I was wondering why it did not work and if that is justified. OK Quote: So, is it a bug in GCC or is my code simply wrong? Your code is simply wrong (as are your assumptions). Every name is looked up during the syntax check of the template (you don't have it instantiated, so no other check is done). In the expression in question, there is a name of a namespace on the left of the assignment operator. Obviously, yes. But how can the compiler know for sure that this name does refer to a namespace while instantiation might change that? Because the namespace is the first name found (since it's the first name available in all scopes searched). Instantiation will NOT change that. Quote: Is that kind of name checking founded in ISO C++ or is it just the usual way to do things in a C++ compiler? Of course it is founded in ISO C++. Why do you think compiler creators do it that way, out of spite? Out of malice? See 3.4.1 for more info. Victor Back to top Bernd Fuhrmann Guest Posted: Sat Dec 27, 2003 9:54 pm    Post subject: Re: Code question that involves namespaces, templates and cl Victor Bazarov wrote: Quote: Because the namespace is the first name found (since it's the first name available in all scopes searched). Instantiation will NOT change that. Obvious. But my point is: Is it a good idea to do have name checking (or whatever you would like to call the step of looking up "Namespace" and finding a namespace) when there are not yet all scopes available since there? You could also see it the other way round: Is it wise to use a fundamently different name-capsule-priority in templates than in normal classes (where inner elements override any outer elements in case of naming conflicts). It doesn't seem to me. Btw: When you change class TBeta : public TAlpha<TSomeType> to class TBeta : public TAlpha<int> it compiles with no complains. So where is the logic in having a look into TAlpha's name scope only sometimes (if it is not template class that depends on TBeta's template parameter)? Maybe it is written in the standart after all that way. If it truly is, that certainly might be a point that should (at least in my opinion) improved. Quote: Is that kind of name checking founded in ISO C++ or is it just the usual way to do things in a C++ compiler? Of course it is founded in ISO C++. Why do you think compiler creators do it that way, out of spite? Out of malice? Even programmers that create compilers are capabable of making mistakes. Some of these bugs are hard to find. There are (or at least they were there when I last checked them) some bugs that only appear if you use almost all cool features of C++, like namespaces, inheritance, and so on in almost all C++ compilers I tried (MSVC, GCC, Borland Builder). So some behaviours are implemented in compilers though they are not truly C++ compliant. That is the reason, why I was asking. Quote: See 3.4.1 for more info. 3.4.1 of what (had a look at faq lite, gcc releases, some other faqs)? Back to top Victor Bazarov Guest Posted: Sat Dec 27, 2003 10:31 pm    Post subject: Re: Code question that involves namespaces, templates and cl "Bernd Fuhrmann" <silverbanana (AT) gmx (DOT) de> wrote... Quote: Victor Bazarov wrote: Because the namespace is the first name found (since it's the first name available in all scopes searched). Instantiation will NOT change that. Obvious. But my point is: Is it a good idea to do have name checking (or whatever you would like to call the step of looking up "Namespace" and finding a namespace) when there are not yet all scopes available since there? Yes, it is. Name lookup is already pretty complicated. Introducing another degree of complexity would just make it worse. Quote: You could also see it the other way round: Is it wise to use a fundamently different name-capsule-priority in templates than in normal classes (where inner elements override any outer elements in case of naming conflicts). It doesn't seem to me. Btw: When you change class TBeta : public TAlpha<TSomeType to class TBeta : public TAlpha it compiles with no complains. So where is the logic in having a look into TAlpha's name scope only sometimes (if it is not template class that depends on TBeta's template parameter)? Since 'TSomeType' is unknown, the TAlpha template specialisation than the original one. Let me illustrate. Imagine that I have template<class A> struct AA { int a; }; template<class B> struct BB : AA<B> { int foo() { return a; } }; template<> struct AA<int> { int b; }; Now, what is 'a' in BB? It is _impossible_ to tell because it depends on what the template argument is. If 'B' is 'int', there _is_no_ 'a'. Quote: Maybe it is written in the standart after all that way. If it truly is, that certainly might be a point that should (at least in my opinion) improved. Then you should go argue about it in 'comp.std.c++'. It makes no sense doing it here, while there is a whole different place _devoted_ to the discussions like that. Quote: See 3.4.1 for more info. 3.4.1 of what (had a look at faq lite, gcc releases, some other faqs)? The Standard. Get yourself a copy and study it before even considering making suggestions about it. Just a friendly advice. Victor Back to top Bernd Fuhrmann Guest Posted: Sun Dec 28, 2003 8:07 am    Post subject: Re: Code question that involves namespaces, templates and cl Victor Bazarov wrote: Quote: Then you should go argue about it in 'comp.std.c++'. It makes no sense doing it here, while there is a whole different place _devoted_ to the discussions like that. Ok, you are right. I'll make a posting there. Quote: See 3.4.1 for more info. 3.4.1 of what (had a look at faq lite, gcc releases, some other faqs)? The Standard. Get yourself a copy and study it before even considering making suggestions about it. Just a friendly advice. Where can I get it (without paying to much money of course)? I always thought that it costs a lot of money (1000$+) to buy it from ISO. I finally think that I should have believed you in first place. Thanks for your patience. Bernd Fuhrmann Back to top Wagner Bruna Guest Posted: Sun Dec 28, 2003 3:10 pm    Post subject: Re: Code question that involves namespaces, templates and cl Hi, Bernd Fuhrmann <silverbanana (AT) gmx (DOT) de> wrote Quote: Victor Bazarov wrote: (...) The Standard. Get yourself a copy and study it before even considering making suggestions about it. Just a friendly advice. Where can I get it (without paying to much money of course)? I always thought that it costs a lot of money (1000$+) to buy it from ISO. You can get a cheaper PDF copy from ANSI. See: http://www.parashift.com/c++-faq-lite/big-picture.html#faq-6.12 -- Wagner Back to top Rob Williscroft Guest Posted: Sun Dec 28, 2003 3:33 pm    Post subject: Re: Code question that involves namespaces, templates and cl Bernd Fuhrmann wrote in news:bsm30o$52v$04$1 (AT) news (DOT) t-online.com: Quote: The Standard. Get yourself a copy and study it before even considering making suggestions about it. Just a friendly advice. Where can I get it (without paying to much money of course)? I always thought that it costs a lot of money (1000$+) to buy it from ISO. I finally think that I should have believed you in first place. Thanks for your patience. Amazon (.co.uk) have a paper version £24.47 http://tinyurl.com/3dse6 You can get the previuos version for $18 in pdf form from ANSI, maybe in the future you will be able to get the current version from them at a resonable price too (last time I checked it was $200+). Rob. -- http://www.victim-prime.dsl.pipex.com/ Back to top Display posts from previous: All Posts1 Day7 Days2 Weeks1 Month3 Months6 Months1 Year Oldest FirstNewest First         C++Talk.NET Forum Index -> C++ language (comp.lang.c++) All times are GMT Page 1 of 1   Jump to: Select a forum C/C++----------------C LanguageC Language (Moderated)C++ Language (Moderated)C++ language (comp.lang.c++)C++ language, library and standards Non-English C/C++ Newsgroups----------------C++ (German)C++ (French)  You cannot post new topics in this forum You cannot reply to topics in this forum You cannot edit your posts in this forum You cannot delete your posts in this forum You cannot vote in polls in this forum Powered by phpBB © 2001, 2006 phpBB Group SEO toolkit © 2004-2006 webmedic.