Zombie Object?

[monarch_dodra]

On Thursday, 7 February 2013 at 10:15:49 UTC, Namespace wrote:
> [code]
> import std.stdio;
>
> class Vec2 {
> public:
> 	short x, y;
> 	
> 	this(short x, short y) {
> 		this.x = x;
> 		this.y = y;
> 	}
> }
>
> void foo(Vec2 v) {
> 	delete v;
> }
>
> void bar(Vec2 v) {
> 	
> }
>
> void main() {
> 	foo(new Vec2(42, 23));
> 	Vec2 v1 = new Vec2(4, 2);
> 	foo(v1);
> 	assert(v1 !is null);
> 	writefln("v1.x = %d", v1.x);
> 	Vec2 v2 = new Vec2(4, 2);
> 	bar(v2);
> 	writefln("v2.x = %d", v2.x);
> }
> [/code]
> This code prints:
> v1.x = 0
> v2.x = 4
>
> But is this correct? I expected
> v1.x = 4
> v2.x = 4
>
> Same behaviour with destroy.

Well, given that you are reading a deleted/destroyed object, I'm 
not sure why you'd expect *any* behavior at all. I'd simply 
expect *undefined* behavior...

In any case, I think what you are seeing is a Vec2 instance init 
state. If you change Vec2 to:

//----
class Vec2 {
public:
	short x = 2, y = 2;
         // ...
//----

Then the output becomes:
v1.x = 2
v2.x = 4

AFAIK, the delete/destroy *might* eagerly reset the object to its 
init state, to make future re-use more efficient. I'm not sure, 
but in any case, what you are observing is undefined, so I 
wouldn't look too much into it...