C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  What is protected inheritance?          C++Talk.NET Forum Index -> C++ Language (Moderated) View previous topic :: View next topic   Author Message PPD Guest Posted: Tue Dec 13, 2005 11:00 pm    Post subject: What is protected inheritance? I understand that public inheritance is "is-a" and private inheritance is "is implemented as". What is protected inheritance? PPD [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Michael Wild Guest Posted: Wed Dec 14, 2005 3:13 am    Post subject: Re: What is protected inheritance? PPD wrote: Quote: I understand that public inheritance is "is-a" and private inheritance is "is implemented as". What is protected inheritance? I actually never thought of it this way, but then you might think of protected members as the "family jewels" Only descendants can access (and override) them. public members are for all to see, access and use. protected members allow this only for direct descendants of a class and private members allow it only for the class itself. There's an exception to this rule: You can define other classes to be a "friend", and thus allow them access to private and protected members. Hope this shed some light on the concept [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top araav Guest Posted: Wed Dec 14, 2005 12:04 pm    Post subject: Re: What is protected inheritance? i think he knows the concept pretty well. it's the mix of the above. "is-a for kids and friends" and "is implemented as" for the others:) [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top kanze Guest Posted: Wed Dec 14, 2005 12:54 pm    Post subject: Re: What is protected inheritance? PPD wrote: Quote: I understand that public inheritance is "is-a" and private inheritance is "is implemented as". That's often true, but there are other uses as well. Quote: What is protected inheritance? Orthogonality? I've never found a particular use for it, either, but it is logical to have it, since we have inheritance for the other access controls as well. -- James Kanze GABI Software Conseils en informatique orientée objet/ Beratung in objektorientierter Datenverarbeitung 9 place Sémard, 78210 St.-Cyr-l'École, France, +33 (0)1 30 23 00 34 [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top PPD Guest Posted: Wed Dec 14, 2005 12:58 pm    Post subject: Re: What is protected inheritance? Thank you for the response. I am misunderstood here. I did not mean protected access. Protected has a good use in terms of limiting member visibility between inherited classes. I appreciate that. My question is about protected inheritance. That is, in the context of: class A { // members }; what is the significance of class B: protected A { .... } Again, I understand how the access restrictions change under protected inheritance. My question is - from design philosophy, what does the protected inheritance mean? I have never had to use this in my code. So I wondered if there is a design scenario that I have always missed out. PPD [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top vord.fok@gmail.com Guest Posted: Wed Dec 14, 2005 7:26 pm    Post subject: Re: What is protected inheritance? Think when you design a project with your private code . And your staff need certain values to use your code . And if you designed your class body right you can implement there side projects in your code properly . thats why you have the 3 types of inherritance . public , private or protected . these are the functions you can call out your base class . ( instance is your call out of your main program ) in private inheritance : memberfunctions private , protected , public instance public (child) memberfunctions protected public (child) instance derrived nothing (grandchild) memberfunction nothing (grandchild) instance derrived nothing in public inheritance : memberfunctions private , protected , public instance public (child) memberfunctions protected public (child) instance derrived public (grandchild) memberfunction protected public (grandchild) instance derrived public protected inheritance : memberfunctions private , protected , public instance public (child) memberfunctions protected public (child) instance derrived nothing (grandchild) memberfunction protected public (grandchild) instance derrived nothing Keeping this in mind you can design projects without ever giving away your own personal code . they only need the memberfunctions and wich tye of inherritance . I hope this is answering your question . Greetings, Smets Jean-Paul [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Diego Martins Guest Posted: Wed Dec 14, 2005 9:03 pm    Post subject: Re: What is protected inheritance? I don't know what is the concept of protected inheritance, but I already used this many times when I implemented mix-in classes in terms of base and pass through the base methods to the subsequent subclasses... consider this: class Matrix {...} class TransformMatrix: protected Matrix { // want to implement in terms of }; class CrazyTransformMatrix: public TransformMatrix { // want to be a TransformMatrix and use useful methods of Matrix }; Cheers Diego Martins [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Augusto KhaoticMind da Si Guest Posted: Thu Dec 15, 2005 10:47 am    Post subject: Re: What is protected inheritance? [email]vord.fok (AT) gmail (DOT) com[/email] wrote: Quote: Think when you design a project with your private code . And your staff need certain values to use your code . And if you designed your class body right you can implement there side projects in your code properly . thats why you have the 3 types of inherritance . public , private or protected . these are the functions you can call out your base class . ( instance is your call out of your main program ) in private inheritance : memberfunctions private , protected , public instance public (child) memberfunctions protected public (child) instance derrived nothing (grandchild) memberfunction nothing (grandchild) instance derrived nothing in public inheritance : memberfunctions private , protected , public instance public (child) memberfunctions protected public (child) instance derrived public (grandchild) memberfunction protected public (grandchild) instance derrived public protected inheritance : memberfunctions private , protected , public instance public (child) memberfunctions protected public (child) instance derrived nothing (grandchild) memberfunction protected public (grandchild) instance derrived nothing Keeping this in mind you can design projects without ever giving away your own personal code . they only need the memberfunctions and wich tye of inherritance . I hope this is answering your question . Greetings, Smets Jean-Paul Another way to put this is that when you do public inheritance, the visibility of the members of your base class is maintained on the child (public is still public, protected is still protected and private is still private), but when you do protected inheritance all public members of the base class become protected in the child while all the rest is is left unchanged. For private inheritance everything becomes private. Now, what does this mean in terms of design i would really love to know as well -- KM [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Matthias Hofmann Guest Posted: Sat Dec 17, 2005 10:58 am    Post subject: Re: What is protected inheritance? "kanze" <kanze (AT) gabi-soft (DOT) fr> schrieb im Newsbeitrag news:1134555084.396549.213850 (AT) g44g2000cwa (DOT) googlegroups.com... Quote: PPD wrote: I understand that public inheritance is "is-a" and private inheritance is "is implemented as". That's often true, but there are other uses as well. What is protected inheritance? Orthogonality? I've never found a particular use for it, either, but it is logical to have it, since we have inheritance for the other access controls as well. I think the answer given by araav comes pretty close: "is-a for kids and friends" and "is implemented as" for the others The interesting part about protected inheritance is that contrary to private inheritance, there is a conversion from the derived class to the base class if the conversion is done in the derived class. Please take a look at the following example: struct A {}; // Note protected inheritance. struct B : protected A { void f( B& b ); }; void f( A& a ) {} void B::f( B& b ) { // Works because B // has access to A. ::f( b ); } int main() { B b; // Does not work because A // is not accessible. f( b ); // Would not work if B::f() // took an A& as its argument. b.f( b ); return 0; } Now how does this fit into the philosophy of object oritented analysis and design? I have no idea... -- Matthias Hofmann Anvil-Soft, CEO http://www.anvil-soft.com - The Creators of Klomanager http://www.anvil-soft.de - Die Macher des Klomanagers [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Seungbeom Kim Guest Posted: Sun Dec 18, 2005 12:41 pm    Post subject: Re: What is protected inheritance? PPD wrote: Quote: I understand that public inheritance is "is-a" and private inheritance is "is implemented as". What is protected inheritance? See this message: http://groups.google.com/group/comp.lang.c++.moderated/msg/f4b765eb77950dfa Hope this helps, -- Seungbeom Kim [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Dave Harris Guest Posted: Mon Dec 19, 2005 10:21 am    Post subject: Re: What is protected inheritance? [email]hofmann (AT) anvil-soft (DOT) com[/email] (Matthias Hofmann) wrote (abridged): Quote: The interesting part about protected inheritance is that contrary to private inheritance, there is a conversion from the derived class to the base class if the conversion is done in the derived class. [...] Now how does this fit into the philosophy of object oritented analysis and design? I have no idea... One way to think of it is that in order to re-implement a derived class that does the same stuff as a base class, it needs to have the same access rights as the base class. If the base class has a conversion to its base, the derived class needs that conversion available too. This is the philosophy followed by languages like Eiffel and Smalltalk. It leads to everything being protected rather than private, and protected inheritance is a natural consequence. C++ does not impose this philosophy, but it does support it. -- Dave Harris, Nottingham, UK. [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. 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