Class and Interface Fun

[John Reimer]

Hello John,

> Hello tim,
> 
>> On Sun, 25 Jan 2009 16:43:55 +1300, John Reimer
>> <terminal.node at gmail.com>  wrote:
>>> With this code:
>>> 
>>> --------------------------------
>>> 
>>> module test5;
>>> 
>>> interface I
>>> {
>>> void foo();
>>> }
>>> class A : I {
>>> void foo() { }
>>> }
>>> class B : A, I
>>> {
>>> alias A.foo foo;
>>> }
>>> void main()
>>> {
>>> }
>>> --------------------------------
>>> I get this error:
>>> 
>>> --------------------------------
>>> 
>>> class test5.B interface function I.foo is not implemented
>>> 
>>> --------------------------------
>>> 
>>> Does this make sense?  I mean, shouldn't the explicit reuse of A.foo
>>> in  B be sufficient indication to the compiler that B is satisfying
>>> the  contract I?   I'm hoping to make use of such subtleties in some
>>> code,  but first I have to understand the reasoning behind this. :)
>>> 
>>> Note that this works if I remove the interface I from B's
>>> declaration --  ie "class B: A" -- since, in the D language, B is
>>> not required to fulfull A's interface contract even though it
>>> inherits from it. -JJR
>>> 
>> It look like the real bug is re-allowing B to implement interface I
>> but
>> sometimes bug do get reported differently. Why don't you remove I
>> from
>> B's
>> declaration like you said that works. It actually says here
>> http://www.digitalmars.com/d/1.0/interface.html "Classes cannot
>> derive
>> from an interface multiple times."
> Yes, please check the link again (further down the page).    D allows
> you to reimplement the interface as long as class B provides a new
> implementation:
> 
> "A reimplemented interface must implement all the interface functions,
> it does not inherit from a super class"...
> 
> That probably could be stated a little more clearly, but that's what
> it says.
> 
> As for why I'm doing it, I assure you that there's a very specific
> reason why I'm trying this: it is a possible interfacing mechansim for
> ported software of a much more complicated nature than this simple
> reduction; I reduced it to this in order to try to understand
> potential iteractions between class and interface layers.  The
> question here was to figure out the reasoning behind the language
> design,  not necessarily whether I should be doing it or not. ;-)
> 
> -JJR
> 


Hmmm, now that I think of it... given the context of my question, I probably 
should have asked it in D newsgroup... 


-JJR