Digital Mars - D - Struct into class

↑ ↓ ← → J Anderson <REMOVEanderson badmama.com.au> writes:

What about the ability to convert a struct to a class.

struct A
{
    int X;
    void method();
}

class B : A
{

}

Would be the same as:

class B
{
    int X;
    void method();
}

You probably wouldn't be able to down cast back to the struct type, and 
it wouldn't work across libraries, but it could be useful when you want 
both a struct and class version of some object.

-Anderson

Dec 16 2003

↑ ↓ ← → Ilya Minkov <minkov cs.tum.edu> writes:

J Anderson wrote:
 What about the ability to convert a struct to a class.


I think this is called automatic boxing: for each struct type, on demand 
a corresponding class type would be automatically created. This would 
allow structs to be direct ancestors of Object, and thus be used in 
polymorfic functions. One example where this can be useful is the 
console inoput/output.

However, if we do that, we could go back and merge struct and class 
*almost* as it was in C++...

-eye

Dec 16 2003

↑ ↓ ← → J Anderson <REMOVEanderson badmama.com.au> writes:

Ilya Minkov wrote:

 J Anderson wrote:

 What about the ability to convert a struct to a class.



 I think this is called automatic boxing: for each struct type, on 
 demand a corresponding class type would be automatically created. This 
 would allow structs to be direct ancestors of Object, and thus be used 
 in polymorfic functions. One example where this can be useful is the 
 console inoput/output.

 However, if we do that, we could go back and merge struct and class 
 *almost* as it was in C++...

 -eye


indirectly referencing the struct, what do you do if you want to use a 
struct as a class.

For instance, I want to extend Burton's (dig) vec3 struct, to add some 
more methods.  I guess I have to use functions instead, or some tacky 
casting :(

-Anderson

Dec 16 2003

↑ ↓ ← → Ilya Minkov <minkov cs.tum.edu> writes:

J Anderson wrote:

 Interesting.  Aside from copying the function interface over or 
 indirectly referencing the struct, what do you do if you want to use a 
 struct as a class.


Indirectly referencing a struct is not a very good option. This would 
mean that toString and toHash cannot be acessed without the source 
expicitly knowing the concrete type of the referenced struct. This means 
that switch would not work correctly, and things like extensible stream 
output were not implementable.

A wrapping class should consist of a struct and have a VTable allowing 
to access struct's methods which correspond to those requiered for a 
Class. We could even allow a struct to inherit from an interface? Then a 
box could automatically implement this interface too, and thus allow for 
high performance stdio, among other uses.

 For instance, I want to extend Burton's (dig) vec3 struct, to add some 
 more methods.  I guess I have to use functions instead, or some tacky 
 casting :(


Current syntax allows to extend a struct. However, what you get is more 
or less a new struct, and even if casting to its predecessor is allowed 
(i don't remember exectly, IMO it should be), as a result you get a "cut 
down" struct of vec3 type, which would not implement the new overridden 
behaviour but the old one. However, as long as you only extend a type, 
everything would work OK.

-eye

-eye

Dec 17 2003

↑ ↓ ← → J Anderson <REMOVEanderson badmama.com.au> writes:

Ilya Minkov wrote:

 J Anderson wrote:

 Current syntax allows to extend a struct. However, what you get is 
 more or less a new struct, and even if casting to its predecessor is 
 allowed (i don't remember exectly, IMO it should be), as a result you 
 get a "cut down" struct of vec3 type, which would not implement the 
 new overridden behaviour but the old one. However, as long as you only 
 extend a type, everything would work OK.

 -eye


Oh, I tried:

struct Vector : vec3
{
   
}

But that didn't work?

I get:
Declaration expected, not ':'

What am I doing wrong

Dec 17 2003