struct vs. class

[Bill Baxter]

Martin wrote:
> Gregor Richards Wrote:
> 
>> Martin wrote:
>>> Inspired by the recent discussion about iterator structs/classes I wanted to ask - what's the design rationale behind having both structs and classes? In C++ the necessity was given by backwards compatibility but that doesn't apply to D of course. 
>>> The only principal differences I can see (I'm not a D programmer (yet), so please correct me if I'm wrong) are a) that structs don't contain run-time meta information (a pointer to a vtable or however that works) and b) that struct variables are statically allocated as opposed to class variables which always seem to be pointers into dynamic memory.
>>> Somehow this looks really unorthogonal to me. Especially b) I find strange, can somebody explain the reason for this?
>>>
>>> cheers
>>> Martin
>> Firstly, your assertion about C++ is incorrect. C++ doesn't have both, 
>> classes are just structs that are private by default, structs are just 
>> classes that are public by default.
> 
> Yes, I know that - still, formally they are two different things (albeit very similar).

And you can tell they're considered different things by the annoying 
fact that if you forward declare a type with the wrong one, the C++ 
compiler will generate an error.

-----
    class Foobulator;

    inline void function(Foobulator& fref) {
       . . .
    }
-----
    struct Foobulator {
       . . .
    };
-----
==> Error Foobulator was declared as a class now it's a struct.

grrr.  I don't care which it is Mr. silly compiler!  And you shouldn't 
either!  All you need to know is that I can make a pointer to the darned 
thing!


--bb