OpEquals and Interfaces

[Steven Schveighoffer]

On Wed, 14 Apr 2010 07:29:28 -0400, Don <nospam at nospam.com> wrote:

> Steven Schveighoffer wrote:
>> On Tue, 13 Apr 2010 19:47:13 -0400, Jason House  
>> <jason.james.house at gmail.com> wrote:
>>
>>> Steven Schveighoffer Wrote:
>>>
>>>> On Tue, 13 Apr 2010 15:50:36 -0400, Christoph Mueller
>>>> <ruunhb at googlemail.com> wrote:
>>>>
>>>> > I'm currently writing a library in D2 which uses intensively  
>>>> interfaces
>>>> > and i meet a problem by overloading the opEquals Operator.
>>>> >
>>>> > In some of my implementations i want to compare an object through an
>>>> > interface of another instance
>>>> >
>>>> > Unfortanetly, the opEquals Operator uses only Object parameters and
>>>> > according to the current DMD-Compiler it's not possible to cast  
>>>> implicit
>>>> > an Interface to an Object. (Got a nice compiler error)
>>>> >
>>>> > Is there any reason to forbid implicit downcasting from any  
>>>> interface to
>>>> > Object?
>>>>
>>>> Any good reason? No.
>>>>
>>>> But the stated reason is usually that interfaces don't necessarily  
>>>> have to
>>>> be Objects, they can be COM objects, which 1) has no bearing in some  
>>>> OSes,
>>>> and 2) does anyone use this feature?
>>>
>>> It could also be a C++ class
>>>
>>  C++ classes are already tagged with extern(C++) (i.e. there's a  
>> difference the compiler can grip to make it behave differently)
>>  Maybe that's the solution, make COM solutions extern(COM), or @COM or  
>> something.  That's fine also.  Anything to then allow the compiler to  
>> assume unadorned interfaces are D objects.
>>  -Steve
>
> I think we can just use extern(C++).

If this is true, this is a no brainer!

This shows my ignorance of COM or why IUnknown is a special interface :)   
If it's just because it's a C++ interface, then yeah, let's set that up.

searching for D's explanation of how COM interfaces work I found this  
really helpful page :P

http://www.digitalmars.com/d/2.0/COM.html

Walter, can you confirm that extern(C++) interfaces are equivalent to  
inheriting IUnknown?  If not, what are the differences?

-Steve