Hi,

I am not able to assign an interface to object. The following code does not compile.

module testObj;

public interface testInterface {
	void someMethod();
}
public class testObj
{
	Object someCaller;
	this(Object caller) {
		someCaller = caller;
	}
	this(testInterface tI, bool xyz) {
		someCaller = tI;
	}
}

Shouldn't this work?

Thanks & Regards
Mandeep

> module testObj;
>
> public interface testInterface {
> 	void someMethod();
> }
> public class testObj
> {
> 	Object someCaller;
> 	this(Object caller) {
> 		someCaller = caller;
> 	}
> 	this(testInterface tI, bool xyz) {
> 		someCaller = tI;
> 	}
> }
>
> Shouldn't this work?

Doesn't really make sense.
If you cast it to Object you "loose" the interface methods.

But it is for only storage purposes. I can cast it back to the Interface later when required.

Thanks
Mandeep

Mandeep Singh Brar <mandeep@brars.co.in> wrote:

> Hi,
>
> I am not able to assign an interface to object. The following code
> does not compile.
>
> module testObj;
>
> public interface testInterface {
> 	void someMethod();
> }
> public class testObj
> {
> 	Object someCaller;
> 	this(Object caller) {
> 		someCaller = caller;
> 	}
> 	this(testInterface tI, bool xyz) {
> 		someCaller = tI;
> 	}
> }
>
> Shouldn't this work?

Nope. D allows interfaces to be special in certain cases (notably COM,
though other may be added in the future), and this precludes making
interfaces implicitly castable to Object.

-- 
Simen

Trass3r <un@known.com> wrote:

>> module testObj;
>>
>> public interface testInterface {
>> 	void someMethod();
>> }
>> public class testObj
>> {
>> 	Object someCaller;
>> 	this(Object caller) {
>> 		someCaller = caller;
>> 	}
>> 	this(testInterface tI, bool xyz) {
>> 		someCaller = tI;
>> 	}
>> }
>>
>> Shouldn't this work?
>
> Doesn't really make sense.
> If you cast it to Object you "loose" the interface methods.

Same way you lose methods of a subclass when you cast it to
a base class. That's allowed, though.

-- 
Simen

On Sat, 15 Jan 2011 11:34:05 -0500, Simen kjaeraas <simen.kjaras@gmail.com> wrote:

> Mandeep Singh Brar <mandeep@brars.co.in> wrote:
>
>> Hi,
>>
>> I am not able to assign an interface to object. The following code
>> does not compile.
>>
>> module testObj;
>>
>> public interface testInterface {
>> 	void someMethod();
>> }
>> public class testObj
>> {
>> 	Object someCaller;
>> 	this(Object caller) {
>> 		someCaller = caller;
>> 	}
>> 	this(testInterface tI, bool xyz) {
>> 		someCaller = tI;
>> 	}
>> }
>>
>> Shouldn't this work?
>
> Nope. D allows interfaces to be special in certain cases (notably COM,
> though other may be added in the future), and this precludes making
> interfaces implicitly castable to Object.

Which unnecessarily complicates things.  For example, you can't compare two interfaces (try it!).

Sorry, had to get my dig in there :P

-Steve

On 15/01/2011 17:44, Steven Schveighoffer wrote:
<snip>
> Which unnecessarily complicates things. For example, you can't compare
> two interfaces (try it!).

?

On 01/15/11 10:34, Simen kjaeraas wrote:
> Mandeep Singh Brar <mandeep@brars.co.in> wrote:
> 
>> Hi,
>>
>> I am not able to assign an interface to object. The following code does not compile.
>>
>> module testObj;
>>
>> public interface testInterface {
>>     void someMethod();
>> }
>> public class testObj
>> {
>>     Object someCaller;
>>     this(Object caller) {
>>         someCaller = caller;
>>     }
>>     this(testInterface tI, bool xyz) {
>>         someCaller = tI;
>>     }
>> }
>>
>> Shouldn't this work?
> 
> Nope. D allows interfaces to be special in certain cases (notably COM, though other may be added in the future), and this precludes making interfaces implicitly castable to Object.
> 

I believe interfaces marked 'extern(C++)' (for using classes defined by
C++) are also somewhat special.

Still, one would think that the special cases (IUnknown and extern(C++)) would be enforced without affecting "typical" interfaces.  Or is there something about how D's vtbl and other affairs are laid out that I don't know about -- such that casting from an interface to Object would lose something?

-- Chris N-S

Stewart Gordon wrote:
> On 15/01/2011 17:44, Steven Schveighoffer wrote:
> <snip>
>> Which unnecessarily complicates things. For example, you can't compare
>> two interfaces (try it!).
> 
> ?
interface I {}

...

I a = ...;
I b = ...;

if (a == b) // <-- ERROR

-- 
mailto:jeberger@free.fr
http://jeberger.free.fr
Jabber: jeberger@jabber.fr

On 16/01/2011 08:23, "Jérôme M. Berger" wrote:
> Stewart Gordon wrote:
>> On 15/01/2011 17:44, Steven Schveighoffer wrote:
>> <snip>
>>> Which unnecessarily complicates things. For example, you can't compare
>>> two interfaces (try it!).
>>
>> ?
> interface I {}
>
> ...
>
> I a = ...;
> I b = ...;
>
> if (a == b) //<-- ERROR


1.065: compiles without error, though it seems to be equivalent to is
2.051: it's really weird
----------
C:\Users\Stewart\Documents\Programming\D\Tests>dmd interface_equals.d
interface_equals.d(7): Error: function object.opEquals (Object lhs, Object rhs)
is not callable using argument types (I,I)
interface_equals.d(7): Error: cannot implicitly convert expression (a) of type i
nterface_equals.I to object.Object
interface_equals.d(7): Error: cannot implicitly convert expression (b) of type i
nterface_equals.I to object.Object
----------

Of course, if the interface declares an opEquals, it's a whole different story....

Stewart.