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D - abstract classes

reply "Martin M. Pedersen" <martin moeller-pedersen.dk> writes:
Hi,

I'm trying to implement a template pattern, but I have problems making it
compile. What I want to do, is something like this:

============================
interface SomeInterface {
    void a();
    void b();
}

class AbstractImpl: SomeInterface {
    void b() { a(); }
}

class Foo: AbstractImpl {
    void a() { printf("foo\n"); }
}

class Bar: AbstractImpl {
    void a() { printf("bar\n"); }
}
============================

But the compiler complains: "class AbstractImpl interface function
SomeInterface.a is not implemented". Of cause it isn't implemented - it
wasn't intended to - it was intended to be abstract. Then I try to
AbstractImpl as:

    abstract class AbstractImpl: SomeInterface { ...

then I get: "function b abstract function cannot have bodies". Maybe
"abstract" on class level applies to all methods in the class? If this is
the case, it is useless, as we have "interface". Then I try to apply
"abstract" to AbstractImpl.a by declaring:

    class AbstractImpl: SomeInterface {
        abstract void a();
        void b() { ...

Now I get the first error message again: "class AbstractImpl interface
function SomeInterface.a is not implemented".


How does one write this?

Is it documented? "abstract" is not documented in
http://www.digitalmars.com/d/attributes.html exect that the attribute
exists, and cannot find it elsewhere.


Regards,
Martin M. Pedersen
Jul 25 2003
parent reply Dario <Dario_member pathlink.com> writes:
Try:

interface SomeInterface {
void a();
void b();
}
class AbstractImpl: SomeInterface {
abstract void a();
void b() { a(); }
}
class Foo: AbstractImpl {
void a() { printf("foo\n"); }
}
class Bar: AbstractImpl {
void a() { printf("bar\n"); }
}
Jul 27 2003
parent "Martin M. Pedersen" <martin moeller-pedersen.dk> writes:
It doesn't work (with DMD 0.68): "class AbstractImpl interface function
SomeInterface.a is not implemented"

"Dario" <Dario_member pathlink.com> wrote in message
news:bg0sgk$2l01$1 digitaldaemon.com...
 Try:

 interface SomeInterface {
 void a();
 void b();
 }
 class AbstractImpl: SomeInterface {
 abstract void a();
 void b() { a(); }
 }
 class Foo: AbstractImpl {
 void a() { printf("foo\n"); }
 }
 class Bar: AbstractImpl {
 void a() { printf("bar\n"); }
 }

Jul 28 2003