Class and Interface Fun
Denis Koroskin
2korden at gmail.com
Sun Jan 25 06:06:50 PST 2009
On Sun, 25 Jan 2009 15:20:19 +0300, Tim M <a at b.com> wrote:
> 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.
No, I don't:
class B : private A, public I
{
}
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