C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  How to prevent a class from being inheritable, in C++          C++Talk.NET Forum Index -> C++ language (comp.lang.c++) View previous topic :: View next topic   Author Message Saumya Guest Posted: Tue Feb 10, 2004 1:08 pm    Post subject: How to prevent a class from being inheritable, in C++ Hi, I didn't know how else to express myself in the subject line, but what I want to know is this: I have a class A, so what do I have to do to ensure that no one can derive from it? Saumya Back to top Hendrik Belitz Guest Posted: Tue Feb 10, 2004 1:10 pm    Post subject: Re: How to prevent a class from being inheritable, in C++ Saumya wrote: Quote: Hi, I didn't know how else to express myself in the subject line, but what I want to know is this: <b>I have a class A, so what do I have to do to ensure that no one can derive from it? Saumya Why do you want to do this? Explaining what you want to achieve with this behaviour would help to find a meaningful solution. -- To get my real email adress, remove the two onkas -- Dipl.-Inform. Hendrik Belitz Central Institute of Electronics Research Center Juelich Back to top Christian Jaeger Guest Posted: Tue Feb 10, 2004 1:24 pm    Post subject: Re: How to prevent a class from being inheritable, in C++ http://www.parashift.com/c++-faq-lite/strange-inheritance.html#faq-23.8 Back to top Philipp Bachmann Guest Posted: Tue Feb 10, 2004 1:50 pm    Post subject: Re: How to prevent a class from being inheritable, in C++ As Christian already posted, there are at least three ways to do so. But: There's no way in C++ as simple as "final" in Java: The first approach needs additional static member functions, the second comment-only approach only works iff the user cooperates, and the third one needs a "friend" declaration in a virtual base class, which isn't nice either. And in my opinion "final"ization imposes a large limitation to the usage of you class. Therefore think twice, please, whether you can't change your design such not to need to make your class behave like "final" any more. Cheers, Philipp. "Saumya" <saumyasarpal (AT) yahoo (DOT) com> wrote Quote: Hi, I didn't know how else to express myself in the subject line, but what I want to know is this: <b>I have a class A, so what do I have to do to ensure that no one can derive from it? Saumya Back to top Karl Heinz Buchegger Guest Posted: Tue Feb 10, 2004 4:18 pm    Post subject: Re: How to prevent a class from being inheritable, in C++ "Philipp Bachmann Quote: As Christian already posted, there are at least three ways to do so. But: There's no way in C++ as simple as "final" in Java: The first approach needs additional static member functions, the second comment-only approach only works iff the user cooperates, and the third one needs a "friend" declaration in a virtual base class, which isn't nice either. And in my opinion "final"ization imposes a large limitation to the usage of you class. Hmm. So it seems I am not alone. All always wondered: Why would one want to impose such a 'finalization' to a class. What is the purpose of doing so? -- Karl Heinz Buchegger [email]kbuchegg (AT) gascad (DOT) at[/email] Back to top Jesper Madsen Guest Posted: Tue Feb 10, 2004 10:35 pm    Post subject: Re: How to prevent a class from being inheritable, in C++ I think the only good reason is to force users of the class to aggregate instead of inherit. Consider a socket implementation, normally a socket class gives no meaning to inherit from, it is like inheriting from std::iostream.. Sure there maybe where it could make sence, but for common use it doesn't.. Jesper "Karl Heinz Buchegger" <kbuchegg (AT) gascad (DOT) at> wrote Quote: "Philipp Bachmann As Christian already posted, there are at least three ways to do so. But: There's no way in C++ as simple as "final" in Java: The first approach needs additional static member functions, the second comment-only approach only works iff the user cooperates, and the third one needs a "friend" declaration in a virtual base class, which isn't nice either. And in my opinion "final"ization imposes a large limitation to the usage of you class. Hmm. So it seems I am not alone. All always wondered: Why would one want to impose such a 'finalization' to a class. What is the purpose of doing so? -- Karl Heinz Buchegger [email]kbuchegg (AT) gascad (DOT) at[/email] Back to top Saumya Guest Posted: Thu Feb 26, 2004 7:55 am    Post subject: Re: How to prevent a class from being inheritable, in C++ Not a very technical reason pal, but it just struck me while I was learning Java and encountered the "final" keyword there. Also, it struck me that what if I was asked this question in some technical interview Back to top Christopher Benson-Manica Guest Posted: Thu Feb 26, 2004 12:53 pm    Post subject: Re: How to prevent a class from being inheritable, in C++ Saumya <saumyasarpal (AT) yahoo (DOT) com> spoke thus: Quote: Not a very technical reason pal, but it just struck me while I was learning Java and encountered the "final" keyword there. http://www.parashift.com/c++-faq-lite/strange-inheritance.html#faq-23.8 Quote: Also, it struck me that what if I was asked this question in some technical interview Just memorize the above URL? ;) -- Christopher Benson-Manica | I *should* know what I'm talking about - if I ataru(at)cyberspace.org | don't, I need to know. Flames welcome. Back to top Razvan Popovici Guest Posted: Thu Feb 26, 2004 10:41 pm    Post subject: Re: How to prevent a class from being inheritable, in C++ I am really wondering who needs such a thing ... Razvan "Christopher Benson-Manica" <ataru (AT) nospam (DOT) cyberspace.org> schrieb im Newsbeitrag news:c1kq80$q3k$1 (AT) chessie (DOT) cirr.com... Quote: Saumya <saumyasarpal (AT) yahoo (DOT) com> spoke thus: Not a very technical reason pal, but it just struck me while I was learning Java and encountered the "final" keyword there. http://www.parashift.com/c++-faq-lite/strange-inheritance.html#faq-23.8 Also, it struck me that what if I was asked this question in some technical interview ;-) Just memorize the above URL? ;) -- Christopher Benson-Manica | I *should* know what I'm talking about - if I ataru(at)cyberspace.org | don't, I need to know. Flames welcome. Back to top Keith H Duggar Guest Posted: Tue Mar 02, 2004 7:15 am    Post subject: Re: How to prevent a class from being inheritable, in C++ Quote: Hmm. So it seems I am not alone. All always wondered: Why would one want to impose such a 'finalization' to a class. What is the purpose of doing so? No you aren't alone. 'finalization' seems almost equivalent to asking: "How can I prevent someone from reusing my code?" The idiom seems to fit well in Java, however. I always do feel like I'm wearing a straight-jacket when I code in Java. So heck, why not 'finalize' the classes to prevent there reuse. After all, you never know when someone (possibly even yourself) might try to reuse it without your permission possibly messing up the aesthetic symmetry your 'pre-planned' class hierarchy. Shame on them. "I have opinions, strong opinions, but, I don't always agree with them." -- G. W. Bush Back to top Datta Patil Guest Posted: Tue Mar 02, 2004 12:45 pm    Post subject: Re: How to prevent a class from being inheritable, in C++ "Saumya" <saumyasarpal (AT) yahoo (DOT) com> wrote Quote: Not a very technical reason pal, but it just struck me while I was learning Java and encountered the "final" keyword there. U mean how to simulate final java class concept in c++.....here is program.I guess its similar to creating singleton pattern // Make ctor private so that class cannot be inheriated //Use static member function to create object of its own which will return ptr to same class obj #include <iostream.h> class X{ private : int x; X(); // private ctor public : static X* getMePrivateObject(); // this will help me creating handle rather for normal object }; X::X(){ cout<<"in constructor"< x=0; }; X* X::getMePrivateObject(){ X *pMyP = new X(); return pMyP; }; /*class Y : public X //cannot do this as X has private ctor { public: Y(){} void print(){ cout<<"Display me if u can";} }; */ void main(void){ X *pMyP = X::getMePrivateObject(); //Rest of ur code } Back to top Datta Patil Guest Posted: Tue Mar 02, 2004 1:10 pm    Post subject: Re: How to prevent a class from being inheritable, in C++ Check this program....Class X acts like final class in java. #include <iostream.h> class X{ private : int x; X(); // private ctor public : static X* getMePrivateObject(); // this will help me creating handle rather for normal object }; X::X(){ cout<<"in constructor"< x=0; }; X* X::getMePrivateObject(){ X *pMyP = new X(); return pMyP; }; /*class Y : public X //cannot do this as X has private ctor { public: Y(){} void print(){ cout<<"Display me if u can";} }; */ void main(void){ X *pMyP = X::getMePrivateObject(); //Rest of ur code } Njoy, Datta Patil 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.