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digitalmars.D.learn - typedefs cannot be used to call superclass members

reply anders runesson.info writes:
Hi there. 
I have 2 classes and two typedefs like so:

file events.d: 
********************
class BEvent {
..
public uint Time() { return time; }
}

class BMouseEvent: BEvent {
..
public int X() { return x; }
public int Y() { return y; }
}

typedef BMouseEvent BMousePressedEvent;
typedef BMouseEvent BMouseReleasedEvent;
***************************

and in my main method I have this:

main.d
**********
..
bool handleEvent(BEvent e) {
BMousePressedEvent ev = cast(BMousePressedEvent) e;

//BMouseEvent ev = cast(BMouseEvent) e; <-- this works
writefln("Event handler called, on ", ev.X, ".", ev.Y, " at ",
ev.Time);                  
return true;
}
***************

When I cast the reference to handleEvent to the typedef
BMousePressedEvent I get the compiler error:

main.d(99): this for X needs to be type BMouseEvent not type
BMousePressedEvent
main.d(99): this for Y needs to be type BMouseEvent not type
BMousePressedEvent
main.d(99): this for Time needs to be type BEvent not type
BMousePressedEvent

The docs say that typedefs can be implicitly converted to their
underlying type, but that doesn't seem to happen. Casting to the
underlying type manually(like the comment does) makes it work.
Any explanation? Am I doing it wrong, or is this a bug?

/Anders
Jul 15 2006
parent Bruno Medeiros <brunodomedeirosATgmail SPAM.com> writes:
anders runesson.info wrote:

 Hi there. 
 I have 2 classes and two typedefs like so:
 
 file events.d: 
 ********************
 class BEvent {
 ...
 public uint Time() { return time; }
 }
 
 class BMouseEvent: BEvent {
 ...
 public int X() { return x; }
 public int Y() { return y; }
 }
 
 typedef BMouseEvent BMousePressedEvent;
 typedef BMouseEvent BMouseReleasedEvent;
 ***************************
 
 and in my main method I have this:
 
 main.d
 **********
 ...
 bool handleEvent(BEvent e) {
 BMousePressedEvent ev = cast(BMousePressedEvent) e;
 
 //BMouseEvent ev = cast(BMouseEvent) e; <-- this works
 writefln("Event handler called, on ", ev.X, ".", ev.Y, " at ",
 ev.Time);                  
 return true;
 }
 ***************
 
 When I cast the reference to handleEvent to the typedef
 BMousePressedEvent I get the compiler error:
 
 main.d(99): this for X needs to be type BMouseEvent not type
 BMousePressedEvent
 main.d(99): this for Y needs to be type BMouseEvent not type
 BMousePressedEvent
 main.d(99): this for Time needs to be type BEvent not type
 BMousePressedEvent
 
 The docs say that typedefs can be implicitly converted to their
 underlying type, but that doesn't seem to happen. Casting to the
 underlying type manually(like the comment does) makes it work.
 Any explanation? Am I doing it wrong, or is this a bug?
 
 /Anders
 
 
 


Yes, it does seem to be a bug. But this notion of "strong-type" typedefs 
of classes is new grounds to me (and likely to many people, are many 
languages which support both notions of OO and strong typedefs?), so it 
is not certain yet.

-- 
Bruno Medeiros - CS/E student
http://www.prowiki.org/wiki4d/wiki.cgi?BrunoMedeiros#D
Jul 16 2006