What would break if class was merged with struct

[Moritz Maxeiner via Digitalmars-d]

On Saturday, 27 May 2017 at 19:26:50 UTC, Ola Fosheim Grøstad 
wrote:
> On Saturday, 27 May 2017 at 19:01:12 UTC, Moritz Maxeiner wrote:
>> Here, `bar`, takes a (pointer to a) class instance as 
>> parameter `foo`. `foo` is a single pointer, i.e. 8 bytes on a 
>> 64bit OS, with *no* special semantics.
>
> Does the language spec say anything about the size of class 
> references?

Yes, is is defined as `ptrsize` and must have the exact same size 
as a pointer to a struct and - more importantly - a pointer to a 
stack frame[1].

>
>> If you want a smart pointer, use one, but don't suddenly make 
>> something that isn't a smart pointer by language design change 
>> shape into a smart pointer.
>
> Is it specified?

Yes, see above link. Unless you make *all* stack frame pointers 
smart pointers (which makes no sense whatsoever), class instances 
cannot be smart pointers in the language as it is specified right 
now.

>
> The common implementation uses a GC, but does it say that an 
> implementation cannot use a reference counted smart pointer or 
> a fat pointer instead?
>
>> Sure, but then type `Foo` in the above must remain a normal 
>> pointer, not become a smart pointer.
>
> That really depends on the definition of the language.

Sure, and the definition requires it.

[1] https://dlang.org/spec/abi.html#delegates