C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Selectively Public Function          C++Talk.NET Forum Index -> C++ language (comp.lang.c++) View previous topic :: View next topic   Author Message zippy747 Guest Posted: Tue Sep 27, 2005 9:34 pm    Post subject: Selectively Public Function I have a high level class X. I have a lower level utility class Y. I want only class X to have access to method y in class Y. i.e. I want class Z to have access to most methods in Y but not method y. Without making y private and making class X a friend of Y, is there a pattern to achieve desired results? Technically, class Y should have no idea of class X so declaring class X as a friend breaks the hierarchy. Thanks, -zip Back to top Victor Bazarov Guest Posted: Tue Sep 27, 2005 9:51 pm    Post subject: Re: Selectively Public Function zippy747 wrote: Quote: I have a high level class X. I have a lower level utility class Y. I want only class X to have access to method y in class Y. i.e. I want class Z to have access to most methods in Y but not method y. Without making y private and making class X a friend of Y, is there a pattern to achieve desired results? Technically, class Y should have no idea of class X so declaring class X as a friend breaks the hierarchy. Something like this? class Y { friend class yBuddy; // whatever that is void y(); public: void yy(); void yyy(); }; class yBuddy { // ah, that's what it is... static void y(Y& a_y) { a_y.y(); } friend class X; // aha! }; class X { void bar(Y& a_y) { a_y.yy(); a_y.y(); // error yBuddy::y(a_y); // a "work-around" } }; class Z { void bar(Y& a_y) { a_y.yy(); a_y.y(); // error yBuddy::y(a_y); // error } }; V Back to top Kai-Uwe Bux Guest Posted: Tue Sep 27, 2005 10:29 pm    Post subject: Re: Selectively Public Function zippy747 wrote: Quote: I have a high level class X. I have a lower level utility class Y. I want only class X to have access to method y in class Y. i.e. I want class Z to have access to most methods in Y but not method y. Without making y private and making class X a friend of Y, is there a pattern to achieve desired results? You want Y.y() to be inaccessible by client code. Making the method y() private is the way to go. That *is* what private means. Quote: Technically, class Y should have no idea of class X so declaring class X as a friend breaks the hierarchy. Technically, you want to make an exception for client class X. Since class Y is where access rights are specified, Y *should* be told that class X is different from all other clients. And that is what friend declarations do. Now, why is there a problem? You have a clean way of achieving exactly the effect you desire through standard means of the language that anybody mainting the code in the future will understand. Yet you are searching for a roundabout way of doing the very same thing. It appears to me that your problem is purely philosophical and not technical. Best Kai-Uwe Bux Back to top zippy747 Guest Posted: Wed Sep 28, 2005 1:08 am    Post subject: Re: Selectively Public Function Are we still pals? -zip Back to top Kai-Uwe Bux Guest Posted: Wed Sep 28, 2005 9:47 pm    Post subject: Re: Selectively Public Function zippy747 wrote: Quote: Are we still pals? Sorry, I didn't mean to be rude. To make up for it, let me elaborate a little bit on the suggestion of Victor Bazarov. To me it seems that the idiom he suggested solves a slightly different problem: how do I make some private members but not all of them available to a class. Consider: class Y { friend class yBuddy; // whatever that is void y(); friend class yyBuddy; // whatever that is void yy(); public: void yyy(); }; class yBuddy { // ah, that's what it is... static void y(Y& a_y) { a_y.y(); } friend class X; // aha! }; class yyBuddy { // ah, that's what it is... static void yy(Y& a_y) { a_y.yy(); } friend class Z; // aha! }; class X { void bar(Y& a_y) { a_y.yyy(); yBuddy::y(a_y); // work-around yyBuddy::yy(a_y); // error } }; class Z { void bar(Y& a_y) { a_y.yyy(); yBuddy::y(a_y); // error yyBuddy::yy(a_y); // work-around } }; Now, X can call y() and Z can call yy() but X cannot call yy() and Z cannot call y(). In case that is what you need, by all means go for it. However, note that it becomes a little more tricky to maintain this code since now you cannot tell which classes have access to the internals of Y just by looking at the code of Y. The definitions of access rights gets somewhat spread out. Best Kai-Uwe Bux Back to top zippy747 Guest Posted: Thu Sep 29, 2005 3:03 am    Post subject: Re: Selectively Public Function You weren't rude. I appreciate your responses. In order to maintain hierarchy, I made another class at the Y hierarchy level -- class Y'. Y' is a friend to class Y and can access its private members. Class X inherits from Class Y' and thus can use base class Y' to access class Y private members. I maintain hierarchy and limit access to class Y private members to classes that inherit from Y'. -zip 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.