C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  RTTI? What about CTTI?          C++Talk.NET Forum Index -> C++ Language (Moderated) View previous topic :: View next topic   Author Message Nicolas Fleury Guest Posted: Wed Oct 22, 2003 8:03 pm    Post subject: RTTI? What about CTTI? Hi, I've seen some discussions about extending current RTTI capabilities on this newsgroup, but RTTI has a cost at run-time, at least in memory, so it always difficult to evaluate what should be added. With a proposal like "metacode", to execute code at compile-time, I wonder if it would be a could idea to provide compile-time type information (I have no idea if CTTI is an existing term) that could be useful when, for example, generating documentation or building layers for other languages (like Boost.Python). What do you think? Regards, Nicolas Fleury [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top David Abrahams Guest Posted: Thu Oct 23, 2003 3:00 pm    Post subject: Re: RTTI? What about CTTI? Nicolas Fleury <nid_oizo (AT) yahoo (DOT) com_remove_the_> writes: Quote: Hi, I've seen some discussions about extending current RTTI capabilities on this newsgroup, but RTTI has a cost at run-time, at least in memory, so it always difficult to evaluate what should be added. With a proposal like "metacode", to execute code at compile-time, I wonder if it would be a could idea to provide compile-time type information (I have no idea if CTTI is an existing term) that could be useful when, for example, generating documentation or building layers for other languages (like Boost.Python). What do you think? You mean like [url]http://www.mail-archive.com/boost (AT) lists (DOT) boost.org/msg09098.html?[/url] I'm for it, of course! -- Dave Abrahams Boost Consulting www.boost-consulting.com [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top sashan Guest Posted: Thu Oct 23, 2003 9:18 pm    Post subject: Re: RTTI? What about CTTI? Nicolas Fleury wrote: Quote: Hi, I've seen some discussions about extending current RTTI capabilities on this newsgroup, but RTTI has a cost at run-time, at least in memory, so it always difficult to evaluate what should be added. With a proposal like "metacode", to execute code at compile-time, I wonder if it would be a could idea to provide compile-time type information (I have no idea if CTTI is an existing term) that could be useful when, for example, generating documentation or building layers for other languages (like Boost.Python). What do you think? gcc implements something called typeof. http://gcc.gnu.org/onlinedocs/gcc/Typeof.html. It's a non-standard extension. -- sashan http://www.cs.auckland.ac.nz/~sgov008/ [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top David B. Held Guest Posted: Fri Oct 24, 2003 12:23 am    Post subject: Re: RTTI? What about CTTI? "Nicolas Fleury" <nid_oizo (AT) yahoo (DOT) com_remove_the_> wrote Quote: [...] (I have no idea if CTTI is an existing term) that could be useful when, for example, generating documentation or building layers for other languages (like Boost.Python). What do you think? I think the term you're looking for is "reflection". You get some of that with Boost.TypeTraits, but that is obviously limited by what is allowed in the language (though in some places, it uses a few suspect tricks that seem to work on some compilers, but might not be strictly "allowed" by the language). Static metaprogramming in general (as opposed to what Lisp does, for instance) in an imperative language (as opposed to say, Haskell or ML) seems to be a bit elusive. It's primitive at best in C++, which tells me that we need "C++ with metaclasses". Who knows...maybe someone will invent such a language. Whatever it is, I know that it isn't D. ;) Dave --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system ([url]http://www.grisoft.com)[/url]. Version: 6.0.521 / Virus Database: 319 - Release Date: 9/23/2003 [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Aaron Bentley Guest Posted: Fri Oct 24, 2003 7:12 pm    Post subject: Re: RTTI? What about CTTI? David B. Held wrote: Quote: Static metaprogramming in general (as opposed to what Lisp does, for instance) in an imperative language (as opposed to say, Haskell or ML) seems to be a bit elusive. It's primitive at best in C++, which tells me that we need "C++ with metaclasses". Who knows...maybe someone will invent such a language. Whatever it is, I know that it isn't D. Daveed Vandevoorde is working on a C++ extension called "metacode", which seems to be along these lines... http://www.vandevoorde.com/Daveed/News/ Aaron -- Aaron Bentley www.aaronbentley.com [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top stelios xanthakis Guest Posted: Fri Oct 24, 2003 7:24 pm    Post subject: Re: RTTI? What about CTTI? Nicolas Fleury <nid_oizo (AT) yahoo (DOT) com_remove_the_> wrote Quote: Hi, I've seen some discussions about extending current RTTI capabilities on this newsgroup, but RTTI has a cost at run-time, at least in memory, so it always difficult to evaluate what should be added. With a proposal like "metacode", to execute code at compile-time, I wonder if it would be a could idea to provide compile-time type information (I have no idea if CTTI is an existing term) that could be useful when, for example, generating documentation or building layers for other languages (like Boost.Python). What do you think? Do you mean like C99 __func__? We could have __class__, __namespace__ and __template__ which shall be special strings in which the compiler shall put the name of the current class, namespace, template? That's an easy solution. "metacode" on the other hand is more challenging, but ... you are talking about an interpreter inside the compiler. So this interpreter should'd better not be a language like C++. It'd better be like python (without the whitespace damage:). It should also communicate with the internal parser. And to provide what?... If the only interesting things are __class__, __template__, __namespace__, __func__ then an entire interpreter is not worth the trouble. metacode not a good idea IMO. I hope I understood CTTI. BTW, RTTI is not just about showing pretty names. It is essential in implementing dynamic_cast and downcasting in virtual inheritance. The thing with the names is just an add-on. I'm against that one too... stelios. [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Nicolas Fleury Guest Posted: Sat Oct 25, 2003 8:30 am    Post subject: Re: RTTI? What about CTTI? stelios xanthakis wrote: Quote: Do you mean like C99 __func__? We could have __class__, __namespace__ and __template__ which shall be special strings in which the compiler shall put the name of the current class, namespace, template? A class is not an object in C++ (in comparison with languages like Python), so suppose your want to iterate through all the classes in a scope and through all member functions of these classes. The question is what is done at run-time and what is done at compile-time. Quote: That's an easy solution. "metacode" on the other hand is more challenging, but ... you are talking about an interpreter inside the compiler. So this interpreter should'd better not be a language like C++. It'd better be like python (without the whitespace damage:). It should also communicate with the internal parser. And to provide what?... If the only interesting things are __class__, __template__, __namespace__, __func__ then an entire interpreter is not worth the trouble. metacode not a good idea IMO. To me, metacode sounds like a kick-ass feature. I'm not sure C++ is a good metaprogramming language (I would more think about something like Lisp), but we need a simpler way to do metaprogramming and we need a way to do more. With other languages rising, C++ is becoming the tool of choice mainly for system programming, video games, etc. where performance is very important. What can be more performant at run-time than doing the maximum at compile-time? Quote: I hope I understood CTTI. BTW, RTTI is not just about showing pretty names. It is essential in implementing dynamic_cast and downcasting in virtual inheritance. The thing with the names is just an add-on. I'm against that one too... I know, and that's why everything that could be done at compile-time should. Adding information to RTTI would be a cost to everyone, not CTTI. Regards, Nicolas Fleury [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. 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