On 2012-12-04 09:22, Maxim Fomin wrote:
And what happens if nobody implements an interface?
import std.stdio;
interface I { }
class A { }
void main()
{
I i;
// assume this is implicit
Object o = cast(Object)i;
writeln(typeid(o));
}
You get a segmentation fault since both "i" and "o" are null.
Safe conversion class to interface requires two conditions:
1a) that class implements interface
1b) if you try to use interface variable, it must be an allocated class
instance
Safe conversion to Object requires:
2a) somebody in class hierarchy implements interface
2b) interface instance is actually allocated class instance
You cannot really get an instance of an interface without having a class
implementing it. That is, without inserting any explicit casts, which works:
interface I { }
class A { }
void main()
{
A a = new A;
I i = cast(I) a;
Object o = cast(Object)i;
writeln(typeid(a)); // A
}
It is possible to check 1a) but impossible in general case to check 2a).
Also the first is design feature while the second is design abuse.
I don't understand why it wouldn't be safe to allow implicit casts of
interfaces to Object.
If I want to call toString, why should I need to insert an explicit cast
to Object just because I have an interface?
--
/Jacob Carlborg
