Multiple Inheritance of Classes

[Steven Schveighoffer]

"superdan" wrote
> Lars Ivar Igesund Wrote:
>
>> Chris R. Miller wrote:
>>
>> > Understand, I'm NOT demanding ANYTHING.
>> >
>> > What is the current state of thought about Multiple Inheritance for
>> > classes in D?  I'd like to have that feature, since it'd make some 
>> > stuff
>> > I want to do a bit easier.  Is it not there because it's not worth the
>> > effort to implement?  Because it's evil and needs to die (I don't know,
>> > some people could possibly be adamantly anti-MI)?
>>
>> This is actually the reason, not the adamantly anti-MI part, just that MI 
>> is
>> evil and that is well acknowledged almost everywhere. You will find good
>> argumentation against it if you look, too.
>
> appeal to authority. appeal to ridicule. appeal to the majority. all in 
> one sentence. wow. at least could you space out your fallacies a bit more.
>
> the man has kindly asked a sensible question. he deserves a good answer. 
> if u can't give one just don't reply. this is just ignorance.

This kind of bullying bullshit does nothing to further communication, or 
help anyone in the least.  You've managed to call many of the brightest 
developers for D idiots, usually based on useless crap like this (which has 
no bearing on anything).  So shut the fuck up.

> below's an attempt at an answer.

Good answer.

> interfaces could implement functions. that does make a lot of sense. 
> example:
>
> interface Customer
> {
>    string ssn();
>    string name();
>    string uniqueName() { return name ~ "(ssn: " ~ ssn ~ ")"; }
> }
>
> so uniqueName formats a specific way. a descendant can choose to change 
> that or just use the default. no idea why walt chose to disallow that. 
> walt?

What do you pass as the 'this' pointer?  When you call a function on an 
interface, the compiler uses the offset of an interface to the 'this' 
pointer to get to the object, but in this case, there is no object, so what 
does the compiler do to call the ssn() and name() functions while 
implementing this function?

If you pass the interface pointer as the 'this' pointer, then how do you 
override it in an Object that implements the interface?  The function in the 
concrete class can't be passed the interface pointer, so you can't really 
override it.

One possible solution is to mark uniqueName as 'final', which means it 
cannot be overridden.  Then you can safely pass the interface pointer to the 
function (casting to the interface if necessary).  This might be a handy 
thing when you always want to implement the same function in all concrete 
classes in terms of the interface functions.

-Steve