C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  separation of pointer types          C++Talk.NET Forum Index -> C++ language, library and standards View previous topic :: View next topic   Author Message christopher diggins Guest Posted: Mon Apr 11, 2005 5:57 pm    Post subject: separation of pointer types What is currently referred to as a pointer in C++ is in my opinion several different types inappropriately amalgamated as one. Consider how there are four very clear categories of pointers with entirely different interfaces: 1) the result of an address-of operation - supports indirection - supports comparison - increment/decrement undefined - delete undefined - delete[] undefined 2) reference to an element of an array - supports indirection - supports comparison - supports increment/decrement - delete undefined - delete[] undefined 3) reference to a dynamically allocated array - supports indirection - supports comparison - supports delete[] - delete undefined 4) reference to a dynamically allocated object - supports indirection - supports comparison - delete[] undefined - supports delete I see no reason these four cases should not each have a separate type. Does anyone else find the the hypothetical idea of separation of pointers into different types to have some allure? -- Christopher Diggins Object Oriented Template Library (OOTL) http://www.ootl.org --- [ comp.std.c++ is moderated. To submit articles, try just posting with ] [ your news-reader. If that fails, use mailto:std-c++@ncar.ucar.edu ] [ --- Please see the FAQ before posting. --- ] [ FAQ: http://www.jamesd.demon.co.uk/csc/faq.html ] Back to top Thomas Maeder Guest Posted: Tue Apr 12, 2005 9:49 am    Post subject: Re: separation of pointer types [email]cdiggins (AT) videotron (DOT) ca[/email] ("christopher diggins") writes: Quote: What is currently referred to as a pointer in C++ is in my opinion several different types inappropriately amalgamated as one. Consider how there are four very clear categories of pointers with entirely different interfaces: 1) the result of an address-of operation - supports indirection - supports comparison - increment/decrement undefined - delete undefined - delete[] undefined 2) reference to an element of an array - supports indirection - supports comparison - supports increment/decrement - delete undefined - delete[] undefined 3) reference to a dynamically allocated array - supports indirection - supports comparison - supports delete[] - delete undefined 4) reference to a dynamically allocated object - supports indirection - supports comparison - delete[] undefined - supports delete I see no reason these four cases should not each have a separate type. Backward compatibility is a very strong reason. Quote: Does anyone else find the the hypothetical idea of separation of pointers into different types to have some allure? Yes. Which is why we have a plethora of smart pointer and container types that take care of cases 3) and 4). The difference between 1) and 2) is blurry, by the way: void f(int &i) { some_pointer_type pi(&i); } int main() { int i(0); f(i); int is[2] = { 0 }; f(is[1]); } --- [ comp.std.c++ is moderated. To submit articles, try just posting with ] [ your news-reader. If that fails, use mailto:std-c++@ncar.ucar.edu ] [ --- Please see the FAQ before posting. --- ] [ FAQ: http://www.jamesd.demon.co.uk/csc/faq.html ] Back to top John Nagle Guest Posted: Tue Apr 12, 2005 9:50 am    Post subject: Re: separation of pointer types christopher diggins wrote: Quote: What is currently referred to as a pointer in C++ is in my opinion several different types inappropriately amalgamated as one. I tend to agree, but it's one of those things that's too late to fix in this language. C++ has the needed concepts: arrays, iterators, and references. But they're all convertable to and from pointers, and most programmers don't see them as distinct. The array-as-pointer thing and the concept of pointer arithmetic are there mostly because they mapped well to PDP-11 hardware. Nobody has put that in a new language in a long time. John Nagle Animats --- [ comp.std.c++ is moderated. To submit articles, try just posting with ] [ your news-reader. If that fails, use mailto:std-c++@ncar.ucar.edu ] [ --- Please see the FAQ before posting. --- ] [ FAQ: http://www.jamesd.demon.co.uk/csc/faq.html ] Back to top kuyper@wizard.net Guest Posted: Wed Apr 13, 2005 6:52 am    Post subject: Re: separation of pointer types christopher diggins wrote: Quote: What is currently referred to as a pointer in C++ is in my opinion several different types inappropriately amalgamated as one. Consider how there are four very clear categories of pointers with entirely different interfaces: 1) the result of an address-of operation - supports indirection - supports comparison - increment/decrement undefined Incorrect; increment is allowed, decrement isn't. Quote: - delete undefined - delete[] undefined 2) reference to an element of an array - supports indirection - supports comparison - supports increment/decrement Decrement is not allowed for a pointer to the first element of an array. Quote: - delete undefined - delete[] undefined 3) reference to a dynamically allocated array - supports indirection - supports comparison You left out: - supports increment Quote: - supports delete[] - delete undefined 4) reference to a dynamically allocated object - supports indirection - supports comparison You left out: - supports increment Quote: - delete[] undefined - supports delete Notice: the (corrected) differences with regard to increment and decrement are all covered by one principle: a pointer to a single object is treated as a pointer to the only element of a 1-element array. It's never legal to decrement a pointer to the first element of an array. It's always legal to increment a pointer to an element of an array. Quote: I see no reason these four cases should not each have a separate type. Does anyone else find the the hypothetical idea of separation of pointers into different types to have some allure? You'll have to identify the advantages. I don't see any. --- [ comp.std.c++ is moderated. To submit articles, try just posting with ] [ your news-reader. If that fails, use mailto:std-c++@ncar.ucar.edu ] [ --- Please see the FAQ before posting. --- ] [ FAQ: http://www.jamesd.demon.co.uk/csc/faq.html ] Back to top Dave Thompson Guest Posted: Mon Apr 18, 2005 5:49 pm    Post subject: Re: separation of pointer types On Tue, 12 Apr 2005 09:50:32 GMT, [email]nagle (AT) animats (DOT) com[/email] (John Nagle) wrote: <snip> Quote: The array-as-pointer thing and the concept of pointer arithmetic are there mostly because they mapped well to PDP-11 hardware. Nobody has put that in a new language in a long time. Actually they mapped better onto the word machines where BCPL was first implemented, like PDP-10 and I think 709x. AIUI it was actually the PDP-11's need for differing strides that drove _reintroduction_ of types into C over B, but without dropping pointer arithmetic which has since been such an opportunity for, ahem, infelicities. Have there been any new SILs, but Oberon by Wirth who always goes for safe? The entire category seems to have fallen out of favor. - David.Thompson1 at worldnet.att.net --- [ comp.std.c++ is moderated. To submit articles, try just posting with ] [ your news-reader. If that fails, use mailto:std-c++@ncar.ucar.edu ] [ --- Please see the FAQ before posting. --- ] [ FAQ: http://www.jamesd.demon.co.uk/csc/faq.html ] 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, library and standards 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.