Re: Why an abstract pointer cannot be used as value in an associate array?

2011-09-30 Thread Christophe 
Cheng Wei , dans le message (digitalmars.D.learn:29865), a écrit :
 Thanks a lot. This solves the problem.
 
 However, it breaks the abstractness. Now in D side, we can call
 auto v = ab(). This does not make sense, because then v cannot be used
 in the C library.
 
 I don't understand why when we manipulate AB*, D compiler needs to know
 the size of struct ab. Moreover, when we use AB*[int], the D compiler
 complains about there's no opHash defined for AB. I don't think they are
 necessary at all.

I guess D is not designed to use abstract classes because they are not 
needed in the language: the compiler reads all the symbols in the file 
before doing the real compilation, but there may be no real issue for 
the compiler, as long as you do not use the ab* for anything else than 
passing it to C code.
 
You could file an enhancement request to support abstract pointer for 
the sake of interoperability with C.

-- 
Christophe

Re: Why an abstract pointer cannot be used as value in an associate array?

2011-09-29 Thread Christophe 
what is the error message ?

Re: Why an abstract pointer cannot be used as value in an associate array?

2011-09-29 Thread Trass3r 

Am 29.09.2011, 06:51 Uhr, schrieb Cheng Wei riverch...@gmail.com:


extern(C) {
struct ab;
}

ab*[int] map;

void main() {
map.clear();
}


Cannot be compiled. Why?

Thanks.


Just use void* for opaque pointers in D.

Re: Why an abstract pointer cannot be used as value in an associate array?

2011-09-29 Thread Timon Gehr 

On 09/29/2011 01:28 PM, Trass3r wrote:

Am 29.09.2011, 06:51 Uhr, schrieb Cheng Wei riverch...@gmail.com:


extern(C) {
struct ab;
}

ab*[int] map;

void main() {
map.clear();
}


Cannot be compiled. Why?

Thanks.


Just use void* for opaque pointers in D.


Or an empty struct.

struct ab{}

Re: Why an abstract pointer cannot be used as value in an associate array?

2011-09-29 Thread Cheng Wei 
The problem is that the void* cannot convert back to AB* when we want to
use it in c library.

Just don't understand why the cast(AB*)p (p is void *) needs to know the
size of AB. Is there any unsafe cast which can blindly cast the
pointers?

Re: Why an abstract pointer cannot be used as value in an associate array?

2011-09-29 Thread Cheng Wei 
Thanks a lot. This solves the problem.

However, it breaks the abstractness. Now in D side, we can call
auto v = ab(). This does not make sense, because then v cannot be used
in the C library.

I don't understand why when we manipulate AB*, D compiler needs to know
the size of struct ab. Moreover, when we use AB*[int], the D compiler
complains about there's no opHash defined for AB. I don't think they are
necessary at all.

Re: Why an abstract pointer cannot be used as value in an associate array?

2011-09-28 Thread bearophile 
Cheng Wei:

 extern(C) {
 struct ab;
 }
 
 ab*[int] map;
 
 void main() {
 map.clear();
 }
 
 
 Cannot be compiled. Why?

It's not specific of associative arrays:

extern(C) {
struct AB;
}
AB*[] arr;
void main() {
arr.length += 1;
}

Bye,
bearophile