Is there a way in D to make sure that interface methods are correctly overridden in subclasses?


class ListenerIFace
{
  void somethingChanged(int data, int data2);
};


class ChangeListener : public ListenerIFace
{
  // does not override the above method
  void somethingChanged(float data, int data2);
};

In face this problem in a current C++ project and the only thing you can do is making the interface method pure virtual, so that it MUST be implemented. If the interface changes after someone derived from it, the compiler will spit out errors because not all pure virtuals are implemented. The downside of this is that you must implement ALL methods specified in the interface.

Another possibility would be to make one interface per callback, but that seems cumbersome to me.

And the most convenient way, but also the way with the highest bug-finding time, is to make all methods in the interface non-abstract. This is nice for the user of the interface as they only need to implement the callback they are interested in, but it gives no compile time errors when subclasses have typos in the parameter lists, leaving you with a silently failing program because of uncalled callbacks.

What I am looking for in D is some way to make sure that the method is correctly overridden, but only IF it is overridden. So that not every user of the interface has to override all methods, but the overriden methods should be somehow made safe.

An idea would be to not allow deriving classes to declare a method with a name already present in a parent class. So when the parent class changes the parameter list of a virtual, subclasses won't compile because they declare a method with the same name but a parameter list that is not there in the parent.

Do I make sense? Any other ideas to solve this? Any way D does solve this already maybe?

Regards,
Jörg Rüppel

Jörg Rüppel wrote:
> Is there a way in D to make sure that interface methods are correctly
> overridden in subclasses?
> 
> 
> class ListenerIFace
> {
>   void somethingChanged(int data, int data2);
> };
> 
> 
> class ChangeListener : public ListenerIFace
> {
>   // does not override the above method
>   void somethingChanged(float data, int data2);
> };
> 
> In face this problem in a current C++ project and the only thing you can
> do is making the interface method pure virtual, so that it MUST be
> implemented. If the interface changes after someone derived from it, the
> compiler will spit out errors because not all pure virtuals are
> implemented. The downside of this is that you must implement ALL methods
> specified in the interface.
> 
> Another possibility would be to make one interface per callback, but
> that seems cumbersome to me.
> 
> And the most convenient way, but also the way with the highest
> bug-finding time, is to make all methods in the interface non-abstract.
> This is nice for the user of the interface as they only need to
> implement the callback they are interested in, but it gives no compile
> time errors when subclasses have typos in the parameter lists, leaving
> you with a silently failing program because of uncalled callbacks.
>
> What I am looking for in D is some way to make sure that the method is
> correctly overridden, but only IF it is overridden. So that not every
> user of the interface has to override all methods, but the overriden
> methods should be somehow made safe.

Use the "override" attribute in derived classes to make the compiler ensure that the same signature exists in a parent class:

http://digitalmars.com/d/attribute.html#override


Sean

Sean Kelly wrote:
> 
> 
> Use the "override" attribute in derived classes to make the compiler ensure that the same signature exists in a parent class:
> 
> http://digitalmars.com/d/attribute.html#override

I fail to understand how someone can not fall in love with D.

"Jörg Rüppel" <joerg@sharky-x.de> wrote in message news:dq6of0$1g5m$1@digitaldaemon.com...
> Sean Kelly wrote:
>>
>>
>> Use the "override" attribute in derived classes to make the compiler ensure that the same signature exists in a parent class:
>>
>> http://digitalmars.com/d/attribute.html#override
>
> I fail to understand how someone can not fall in love with D.

LOL!

:-)