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.NET Forum / Languages / C# / March 2008OOP problem: multiple inheritance througt interfaces?
Hi, i have this classes: class Db class SqlDb : Db class OracleDb : Db class DbConverter class SqlDbConverter : DbConverter class OracleDbConverter : DbConverter now, in SqlDbConverter classe i would like to use DbConverter methods AND SqlDb methods, in OracleDbConverter class i would like to use DbConverter methods AND OracleDb methods, this is possible in c++ inherit a class from 2 base classes but with .net i can iherit only from 1 class. this becouse i would use common methods of DbConverter class for SqlDbConverter objects and OracleDbConverter objects AND use common methods of Db class for SqlDb objects and OracleDb objects. now, c# implements multiple interface inheritance but i think it not solve my problem... any help? Thanks! > [...] > this becouse i would use common methods of DbConverter class for [quoted text clipped - 3 lines] > now, c# implements multiple interface inheritance but i think it not > solve my problem... If you want your OracleDbConverter class to itself expose the interface defined by OracleDb and DbConverter class, in a way that allows it to be treated as either class, that's not possible in C#. However, using interfaces certainly is one possible work-around, depending on what you really need to accomplish. If you can create an interface that describes either the Db or DbConverter class (or both), then your OracleDbConverter class can then implement that interface (or interfaces) using composition. That is, inside the OracleDbConverter it would have an instance of the class implementing the interface, which is uses to delegate the handling of the interface to. Then where you would have required the "Db" or "DbConverter" class, instead you can require the relevant interface. Since your OracleDbConverter class would implement the interface, it would be usable there. It's not quite as convenient as true multiple inheritance, but it does avoid some of the complexity that true MI can introduce. Pete > [...] > However, using interfaces certainly is one possible work-around, depending [quoted text clipped - 9 lines] > OracleDbConverter class would implement the interface, it would be usable > there. but with interfaces i have to IMPLEMENT ALL the code also for common methods... my goal is to derive from a common classes and implement only specialized methods. so that SqlDb and OracleDb can use Db methods and SqlDbConverter and OracleDbConverter can use Db and DbConverter methods. there is a work-around for this? Thanks > but with interfaces i have to IMPLEMENT ALL the code also for common > methods... Yes, you do. I did say it's less convenient. The VS IDE will auto-generate the interface stubs for you if you ask it to, but yes...you'll have to go through each one and add the appropriate calls within each stub. > my goal is to derive from a common classes and implement only > specialized methods. > so that > > SqlDb and OracleDb can use Db methods and SqlDbConverter and > OracleDbConverter can use Db and DbConverter methods. I do understand how inheritance of concrete classes works, thank you. I've already explained that C# doesn't support multiple inheritance of classes, and I've already described the alternative. As long as you can restructure your design so that interfaces can be used for your references, rather than actual classes, it will work, albeit with more typing effort on your part. > there is a work-around for this? See above. Pete On Mar 21, 2:50 pm, "Gambero" <cgamberiniNON_VOGLIO_S...@libero.it> wrote: > Hi, i have this classes: > [quoted text clipped - 22 lines] > > any help? Thanks! Can you use composition? SqlDbConverter can instantiate an instance of SqlDb Otherwise you have to rethink your structure >Can you use composition? >SqlDbConverter can instantiate an instance of SqlDb incapsulate a Db object in DbConverter class is a good alternative, but in this way i have to change access modifiers of low-level methods implemented in Db class to public for use in DbConverter methods, and i would like that low-level methods remain private usable only within the class or in derived classes.. thanks for suggestion! any other idea? Thanks >> Can you use composition? >> SqlDbConverter can instantiate an instance of SqlDb [quoted text clipped - 4 lines] > and i would like that low-level methods remain private usable only > within the class or in derived classes.. That's what the "internal" access modifier is for... > thanks for suggestion! > > any other idea? > > Thanks >> incapsulate a Db object in DbConverter class is a good alternative, >> but in this way i have to change access modifiers of low-level methods [quoted text clipped - 3 lines] > > That's what the "internal" access modifier is for... good suggestion, but i have Db, SqlDb and OracleDb in one assembly, and DbConverter, SqlDbConverter and OracleDbConverter in another assembly. internal restrict the visibility only within the current assembly... is not my solution.. Thanks other suggestions? >>> incapsulate a Db object in DbConverter class is a good alternative, >>> but in this way i have to change access modifiers of low-level [quoted text clipped - 12 lines] > > other suggestions? InternalsVisibleToAttribute ?
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