Abstract classes vs interfaces, casting from void*

[John Colvin]

On Sunday, 11 August 2019 at 15:16:03 UTC, Alex wrote:
> On Sunday, 11 August 2019 at 13:09:43 UTC, John Colvin wrote:
>>> Ok. What would go wrong (in D) if I just replaced every 
>>> interface with an abstract class?
>>
>> I think there's some confusion here, because B.foo is not 
>> abstract. abstract on a class is not inherited by its methods. 
>> https://dlang.org/spec/attribute.html#abstract
>
> Now, I'm confused, as you asked about abstract classes. So, 
> yes, you can define the abstractness of classes differently. 
> And what is your point?

I'm trying to narrow down exactly what patterns work with each 
and how they overlap.

What I was trying to get at with the abstract method thing is that

abstract class C
{
     void foo();
}

is an abstract class with a non-abstract method, whose 
implementation is going to come from somewhere else (not a common 
pattern in D).

class C
{
     abstract void foo();
}

is an abstract class with an abstract method foo, which means you 
have to override it in a inheriting class to get a non-abstract 
class.