Class and Interface Fun

[Tim M]

On Mon, 26 Jan 2009 04:58:57 +1300, John Reimer <terminal.node at gmail.com>  
wrote:

> Hello tim,
>
>> On Mon, 26 Jan 2009 01:14:10 +1300, Denis Koroskin <2korden at gmail.com>
>> wrote:
>>
>>> On Sun, 25 Jan 2009 15:06:23 +0300, Tim M <a at b.com> wrote:
>>>
>>>> On Mon, 26 Jan 2009 00:48:21 +1300, Tim M <a at b.com> wrote:
>>>>
>>>>> On Mon, 26 Jan 2009 00:18:28 +1300, Denis Koroskin
>>>>> <2korden at gmail.com>  wrote:
>>>>>
>>>>>> On Sun, 25 Jan 2009 08:38:18 +0300, Tim M <a at b.com> wrote:
>>>>>>
>>>>>>> On Sun, 25 Jan 2009 17:56:03 +1300, John Reimer
>>>>>>> <terminal.node at gmail.com> wrote:
>>>>>>>
>>>>>>>> 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
>>>>>>>>
>>>>>>> This works btw:
>>>>>>>  module test;
>>>>>>>  interface I
>>>>>>> {
>>>>>>> void foo();
>>>>>>> }
>>>>>>> class A : I {
>>>>>>> void foo() { }
>>>>>>> }
>>>>>>> class B : A,I
>>>>>>> {
>>>>>>> void foo() { A.foo(); }
>>>>>>> }
>>>>>>> void main()
>>>>>>> {
>>>>>>> }
>>>>>> It is too verbose and makes twice an overhead. I'd like to avoid
>>>>>> this
>>>>>> solution.
>>>>>> In fact, I believe that class B : A, I {} should just work.
>>>>> why? I think it is perfect how it is. You can either leave A as the
>>>>> class that implements I and B would implement it through
>>>>> inheritance  or you can to re implement I define all new
>>>>> implementations and put in  return super.foo(); where needed. It is
>>>>> also possible to reimplement  one interface function without re
>>>>> implementing the whole interface.
>>>>>
>>>> If you are really needing to write least code you could also do
>>>> something like this but not very nice to read:
>>>>  module test;
>>>>  template II(char[] func)
>>>> {
>>>> const char[] II = "typeof(super." ~ func ~ "())" ~ " " ~ func ~
>>>> "() {  return super." ~ func ~ "(); }" ;
>>>> }
>>>> interface I
>>>> {
>>>> void foo();
>>>> int bar();
>>>> }
>>>> class A : I
>>>> {
>>>> void foo() { }
>>>> int bar() { return 1; }
>>>> }
>>>> class B : A,I
>>>> {
>>>> //void foo() { return super.foo(); }
>>>> mixin(II!("foo"));
>>>> mixin(II!("bar"));
>>>> }
>>>> void main()
>>>> {
>>>> }
>>> Not only I want to write less, I want my code be cleaner and run
>>> faster.
>>>
>>>> why? I think it is perfect how it is. You can either leave A as the
>>>> class that implements I and B would implement it through inheritance
>>>> or  you can to re implement I define all new implementations and put
>>>> in  return super.foo(); where needed. It is also possible to
>>>> reimplement  one interface function without re implementing the
>>>> whole interface.
>>>>
>>> That what /my/ solution do.
>>>  class B : A, I {}
>>>  is *absolutely* same as
>>>  class B : A, I
>>> {
>>> override void foo() { super.foo(); }
>>> override int bar() { return super.bar(); }
>>> }
>>> Except that when you call B.foo, there is no damn double virtual
>>> function call.
>>>  B inherits all the functions from A implicitly. You stil may override
>>> any of the I interface functions if need be:
>>>  class B : A, I
>>> {
>>> override void foo() { ... }
>>> // int bar() is inherited from A
>>> }
>>> Having B explicitly override all the base class virtual functions and
>>> forward them to A implementation just to make compiler happy is
>>> unintuitive and plain dumb to me.
>>>  C# allows that and I see absolutely no reason why D doesn't.
>>>
>> I think you are missing somethinghere. Change the B definition from:
>>  class B : A, I
>>  to just:
>>  class B : A
>>  then interfaces become impicit.
>>
>
>
> What do you mean?  In your example above, B does not have to implement  
> the interface I of A.  What do you mean by "interfaces become implicit"?
>
> -JJR
>
>

I mean it will still have the foo function and you dont have to put  
anything on B to make it work:

module test;



interface I
{
       void foo();
}

class A : I
{
       void foo() { }
}


class B : A
{

}

void main()
{
       B b = new B;
       b.foo(); //this works
}