D versus Objective C Comparison

[Jacob Carlborg]

Michel Fortin wrote:
> On 2009-01-31 20:51:57 -0500, Chris R Miller 
> <lordsauronthegreat at gmail.com> said:
> 
>>> If you had a smart enough dynamic linker and the signature of each 
>>> function in the virtual table, you could do that in D too by creating 
>>> virtual tables and updating offsets in the code accordingly while 
>>> linking. (Objective-C doesn't work like that, but it has the same 
>>> effect.) Alternativly, it could be done in some static initialisation 
>>> phase.
>>
>> An increasingly interesting toy to study (I would think) would be 
>> Categories - the ability to take an existing class and just randomly 
>> tack on additional receivers.  Perhaps this is exclusive to 
>> Objective-C's message-receiver architecture, but it's a curious little 
>> technology nonetheless.
> 
> I'm sure we could add something like categories with what I'm proposing 
> above. In fact, many people on this list have requested a way to write 
> extensions to classes: more methods you can invoke using the dot syntax. 
> Perhaps virtual tables built at runtime could allow people to write 
> class extensions and still be able to override extension methods in 
> subclasses.
> 

It would be great if D could have categories/open classes and you could 
do something like this:

class A
{
     void foo () {}
}

class A
{
     void bar () {}
}

void main ()
{
     auto a = new A;
     a.foo;
     a.bar;
}

And it should of course work on classes you don't have access to the 
source code.