I have a small question: why aren't interfaces implicitly convertible to Object?

-- 
Bye,
Gor Gyolchanyan.

On 27-07-2012 16:56, Gor Gyolchanyan wrote:
> I have a small question: why aren't interfaces implicitly convertible to
> Object?
>
> --
> Bye,
> Gor Gyolchanyan.

I don't know if there's any particular reason, but for what it's worth: Casting an interface to Object means going through its vtable back to the original object location. In other words, it's not "free" (though the cost is extremely minimal).

-- 
Alex Rønne Petersen
alex@lycus.org
http://lycus.org

On Friday, 27 July 2012 at 14:56:18 UTC, Gor Gyolchanyan wrote:
> I have a small question: why aren't interfaces implicitly convertible to
> Object?

Not all interfaces »originate« from D objects, they can also be COM interfaces. Using (cast(Object)foo) should work if foo is really an Object.

David

On Fri, 27 Jul 2012 12:48:59 -0400, David Nadlinger <see@klickverbot.at>
wrote:

> On Friday, 27 July 2012 at 14:56:18 UTC, Gor Gyolchanyan wrote:
>> I have a small question: why aren't interfaces implicitly convertible to
>> Object?
>
> Not all interfaces »originate« from D objects, they can also be COM interfaces. Using (cast(Object)foo) should work if foo is really an Object.

All Com interfaces inherit from IUnknown.  This is statically known.

The idea that we cannot tell which interfaces are COM and which are normal
is a myth.

There is no reason why interfaces (that aren't COM) shouldn't be
implicitly castable to Object.

-Steve

On Friday, 24 August 2012 at 14:15:28 UTC, Steven Schveighoffer wrote:
> On Fri, 27 Jul 2012 12:48:59 -0400, David Nadlinger <see@klickverbot.at>
> wrote:
>
>> On Friday, 27 July 2012 at 14:56:18 UTC, Gor Gyolchanyan wrote:
>>> I have a small question: why aren't interfaces implicitly convertible to
>>> Object?
>>
>> Not all interfaces »originate« from D objects, they can also be COM interfaces. Using (cast(Object)foo) should work if foo is really an Object.
>
> All Com interfaces inherit from IUnknown.  This is statically known.
>
> The idea that we cannot tell which interfaces are COM and which are normal
> is a myth.
>
> There is no reason why interfaces (that aren't COM) shouldn't be
> implicitly castable to Object.
>
> -Steve

Technically true, however COM is not the only example of foreign objects used via interfaces.  The (limited) C++ compatibility, for example, works this way.

On Fri, 24 Aug 2012 22:01:51 -0400, Chris Nicholson-Sauls <ibisbasenji@gmail.com> wrote:

> On Friday, 24 August 2012 at 14:15:28 UTC, Steven Schveighoffer wrote:
>> On Fri, 27 Jul 2012 12:48:59 -0400, David Nadlinger <see@klickverbot.at>
>> wrote:
>>
>>> On Friday, 27 July 2012 at 14:56:18 UTC, Gor Gyolchanyan wrote:
>>>> I have a small question: why aren't interfaces implicitly convertible to
>>>> Object?
>>>
>>> Not all interfaces »originate« from D objects, they can also be COM interfaces. Using (cast(Object)foo) should work if foo is really an Object.
>>
>> All Com interfaces inherit from IUnknown.  This is statically known.
>>
>> The idea that we cannot tell which interfaces are COM and which are normal
>> is a myth.
>>
>> There is no reason why interfaces (that aren't COM) shouldn't be
>> implicitly castable to Object.
>>
>> -Steve
>
> Technically true, however COM is not the only example of foreign objects used via interfaces.  The (limited) C++ compatibility, for example, works this way.

Those are extern(C++), also statically known.

In fact, the very nature of how interfaces work makes it very difficult for us to *not* statically know that an interface is a D interface -- D's implementation of interfaces is not like any others.

-Steve