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

On Sun, 25 Jan 2009 16:43:55 +1300, John Reimer <terminal.node@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."

Hello tim,

> On Sun, 25 Jan 2009 16:43:55 +1300, John Reimer
> <terminal.node@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

Hello John,

> Hello tim,
> 
>> On Sun, 25 Jan 2009 16:43:55 +1300, John Reimer
>> <terminal.node@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

On Sun, 25 Jan 2009 17:56:03 +1300, John Reimer <terminal.node@gmail.com> wrote:

> Hello tim,
>
>> On Sun, 25 Jan 2009 16:43:55 +1300, John Reimer
>> <terminal.node@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()
{
}

Hello tim,

> On Sun, 25 Jan 2009 17:56:03 +1300, John Reimer
> <terminal.node@gmail.com>  wrote:
> 
>> Hello tim,
>> 
>>> On Sun, 25 Jan 2009 16:43:55 +1300, John Reimer
>>> <terminal.node@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()
> {
> }
> 


Yes, I can resort to that if absolutely necessary (but I'd rather not :( ).  I'm curious why doing a much simpler "alias" doesn't work, since it's the D way of making inherited methods accessible to the subclass.

I figured that the "alias" should automatically (re-)implement the interface as well.

-JJR

On Sun, 25 Jan 2009 08:38:18 +0300, Tim M <a@b.com> wrote:

> On Sun, 25 Jan 2009 17:56:03 +1300, John Reimer <terminal.node@gmail.com> wrote:
>
>> Hello tim,
>>
>>> On Sun, 25 Jan 2009 16:43:55 +1300, John Reimer
>>> <terminal.node@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.

On Mon, 26 Jan 2009 00:18:28 +1300, Denis Koroskin <2korden@gmail.com> wrote:

> On Sun, 25 Jan 2009 08:38:18 +0300, Tim M <a@b.com> wrote:
>
>> On Sun, 25 Jan 2009 17:56:03 +1300, John Reimer <terminal.node@gmail.com> wrote:
>>
>>> Hello tim,
>>>
>>>> On Sun, 25 Jan 2009 16:43:55 +1300, John Reimer
>>>> <terminal.node@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.

On Mon, 26 Jan 2009 00:48:21 +1300, Tim M <a@b.com> wrote:

> On Mon, 26 Jan 2009 00:18:28 +1300, Denis Koroskin <2korden@gmail.com> wrote:
>
>> On Sun, 25 Jan 2009 08:38:18 +0300, Tim M <a@b.com> wrote:
>>
>>> On Sun, 25 Jan 2009 17:56:03 +1300, John Reimer <terminal.node@gmail.com> wrote:
>>>
>>>> Hello tim,
>>>>
>>>>> On Sun, 25 Jan 2009 16:43:55 +1300, John Reimer
>>>>> <terminal.node@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()
{
}

On Sun, 25 Jan 2009 15:06:23 +0300, Tim M <a@b.com> wrote:

> On Mon, 26 Jan 2009 00:48:21 +1300, Tim M <a@b.com> wrote:
>
>> On Mon, 26 Jan 2009 00:18:28 +1300, Denis Koroskin <2korden@gmail.com> wrote:
>>
>>> On Sun, 25 Jan 2009 08:38:18 +0300, Tim M <a@b.com> wrote:
>>>
>>>> On Sun, 25 Jan 2009 17:56:03 +1300, John Reimer <terminal.node@gmail.com> wrote:
>>>>
>>>>> Hello tim,
>>>>>
>>>>>> On Sun, 25 Jan 2009 16:43:55 +1300, John Reimer
>>>>>> <terminal.node@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.