D - [BUG] casting from Object to interface
- Ben Hinkle (23/23) Apr 07 2004 based on Kris's interface experiments here is a simple example
- Derek Parnell (5/28) Apr 07 2004 And if you say "class D:C,B {}" instead of "class D:B,C {}", it works fi...
- John Reimer (10/17) Apr 07 2004 I read Kris's document on interfaces. It was very well written, and I
- Phill (8/31) Apr 07 2004 In Java you wouldnt even need to cast that.
- Ben Hinkle (7/8) Apr 08 2004 Umm, do you mean java.lang.Object implicitly casts to anything? It
- Phill (22/32) Apr 08 2004 Nope I meant that you can go straight from
based on Kris's interface experiments here is a simple example
of one of the problems he is talking about. As written below it
will cause an Access Violation. If you either cast from x or
make C extend A instead of B then everything works ok. Something
about dynamic casting from Object to an interface that extends
another interface. I don't know if Kris has already posted an
example like this but I thought I'd go ahead and post anyway.
interface A {}
interface B:A {}
interface C {}
class D:B,C {}
int main()
{
D x = new D();
printf("D: %p\n",x);
Object o = x;
printf("o: %p\n",o);
B b = cast(B)o;
printf("B: %p\n",b);
C c = cast(C)o; // boom
printf("C: %p\n",c);
return 0;
}
Apr 07 2004
"Derek Parnell" <Derek.Parnell psyc.ward>
On Wed, 07 Apr 2004 23:00:20 -0400 (08/Apr/04 01:00:20 PM)
, Ben Hinkle <bhinkle4 juno.com> wrote:
based on Kris's interface experiments here is a simple example
of one of the problems he is talking about. As written below it
will cause an Access Violation. If you either cast from x or
make C extend A instead of B then everything works ok. Something
about dynamic casting from Object to an interface that extends
another interface. I don't know if Kris has already posted an
example like this but I thought I'd go ahead and post anyway.
interface A {}
interface B:A {}
interface C {}
class D:B,C {}
int main()
{
D x = new D();
printf("D: %p\n",x);
Object o = x;
printf("o: %p\n",o);
B b = cast(B)o;
printf("B: %p\n",b);
C c = cast(C)o; // boom
printf("C: %p\n",c);
return 0;
}
And if you say "class D:C,B {}" instead of "class D:B,C {}", it works fine.
--
Derek
Apr 07 2004
Ben Hinkle wrote:based on Kris's interface experiments here is a simple example of one of the problems he is talking about. As written below it will cause an Access Violation. If you either cast from x or make C extend A instead of B then everything works ok. Something about dynamic casting from Object to an interface that extends another interface. I don't know if Kris has already posted an example like this but I thought I'd go ahead and post anyway.I read Kris's document on interfaces. It was very well written, and I learned quite a bit from the short essay. Perhaps it could be improved: for each item in the list of 11 interface uses, it would be nice to have a small example demonstrating the manditory interface application that he mentions. Code sometimes explains what's difficult to comprehend in English. (I understand that some features on the list might not lend themselves well to code examples). Later, John
Apr 07 2004
"Ben Hinkle" <bhinkle4 juno.com> wrote in message
news:4of970hv6g5j93msf30el85ckvs0cg0jtb 4ax.com...
based on Kris's interface experiments here is a simple example
of one of the problems he is talking about. As written below it
will cause an Access Violation. If you either cast from x or
make C extend A instead of B then everything works ok. Something
about dynamic casting from Object to an interface that extends
another interface. I don't know if Kris has already posted an
example like this but I thought I'd go ahead and post anyway.
interface A {}
interface B:A {}
interface C {}
class D:B,C {}
int main()
{
D x = new D();
printf("D: %p\n",x);
Object o = x;
printf("o: %p\n",o);
B b = cast(B)o;
printf("B: %p\n",b);
C c = cast(C)o; // boom
printf("C: %p\n",c);
return 0;
}
In Java you wouldnt even need to cast that.
Phill.
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Apr 07 2004
In Java you wouldnt even need to cast that.Umm, do you mean java.lang.Object implicitly casts to anything? It shouldn't. If the static type is a subclass or implements the type you are casting to then the cast can be implicit in Java and D but otherwise you need to perform a run-time cast. I think D is running into trouble because the run-time cast behavior seems to depend on the static type - which is really wierd. -Ben
Apr 08 2004
"Ben Hinkle" <bhinkle4 juno.com> wrote in message news:c53ja7$11mq$1 digitaldaemon.com...Nope I meant that you can go straight from the class to interface like this: class Test implements Runnable{ public static void main(String[] args) { Test t = new Test(); Runnable r = t; } public void run(){} } As you well know if you wanted to go from Object to interface then you would need to go: Test t = new Test(); Object o = t; Runnable r = (Runnable)o; Phill. --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.648 / Virus Database: 415 - Release Date: 3/31/2004In Java you wouldnt even need to cast that.Umm, do you mean java.lang.Object implicitly casts to anything? It shouldn't. If the static type is a subclass or implements the type you are casting to then the cast can be implicit in Java and D but otherwise you need to perform a run-time cast. I think D is running into trouble because the run-time cast behavior seems to depend on the static type - which is really wierd. -Ben
Apr 08 2004