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D - Bug? partially implemented interfaces

reply Hauke Duden <H.NS.Duden gmx.net> writes:
This may be a compiler bug, or maybe I'm just doing something wrong. The 
following code does not compile:


interface I
{
	void a();
	void b();
}

class Impl : I
{
	void a()
	{
	}
}

The compiler produces the following error:

"class Impl interface function I.b is not implemented."

I want "Impl" to be an abstract class that implements default behaviour 
for some of the interface functions, but leaves other interface 
functions unimplemented.

I have tried adding the line "abstract void b();" to the class 
definition, but that doesn't change anything. Using "abstract class" 
instead of "class" also has no effect on this error.

There doesn't seem to be anything in the docs about how abstract classes 
are done in D, except for the fact that "abstract" is mentioned in the 
keyword list.

So, how can I partially implement an interface in an abstract class?


Hauke
Jan 01 2004
parent reply J C Calvarese <jcc7 cox.net> writes:
Hauke Duden wrote:

 This may be a compiler bug, or maybe I'm just doing something wrong. The 
 following code does not compile:
 
 
 interface I
 {
     void a();
     void b();
 }
 
 class Impl : I
 {
     void a()
     {
     }
 }
 
 The compiler produces the following error:
 
 "class Impl interface function I.b is not implemented."
 
 I want "Impl" to be an abstract class that implements default behaviour 
 for some of the interface functions, but leaves other interface 
 functions unimplemented.
 
 I have tried adding the line "abstract void b();" to the class 
 definition, but that doesn't change anything. Using "abstract class" 
 instead of "class" also has no effect on this error.
 
 There doesn't seem to be anything in the docs about how abstract classes 
 are done in D, except for the fact that "abstract" is mentioned in the 
 keyword list.
 
 So, how can I partially implement an interface in an abstract class?
 
 
 Hauke
 
 


I don't know why your code is illegal, but the following does compile:


interface I
{
     void a();
     void b();
}

class Impl : I
{
     void a()
     {
     }

     void b()
     {
     }

}

class Kid : Impl
{
     void b()
     {
         printf("overriden method\n\0");
     }

}

void main()
{
     Kid k = new Kid();
     k.b();
}


If you want to remind yourself to override the method, you could add an 
"assert(0);" to the method that you want to abstract.

I'm not really sure what your goal is (all this abstract stuff is over 
my head), but I hope this might help.


-- 
Justin
http://jcc_7.tripod.com/d/
Jan 02 2004
parent Hauke Duden <H.NS.Duden gmx.net> writes:
J C Calvarese wrote:

 I don't know why your code is illegal, but the following does compile:
 
 
 interface I
 {
     void a();
     void b();
 }
 
 class Impl : I
 {
     void a()
     {
     }
 
     void b()
     {
     }
 
 }


<snip>


 If you want to remind yourself to override the method, you could add an 
 "assert(0);" to the method that you want to abstract.
 
 I'm not really sure what your goal is (all this abstract stuff is over 
 my head), but I hope this might help.


What I want to do is avoid adding a dummy implementation for b. A dummy 
function with an assert doesn't quite cut it, since then the class could 
be instantiated, even though it is supposed to be abstract. Not to 
mention that this would also be a very dirty hack AND it would make 
another compile-time condition a runtime condition.

D supports abstract classes (right?), so a class that only partially 
implements an interface should simply be abstract. I just don't know how 
to get the compiler to recognize that.

Hauke
Jan 02 2004