Confused about class equality

[Ali Çehreli]

strtr wrote:
> The program below outputs, as I would expect :
> Same Value.
> Same Object.
> 3 : 44E15C 0000
> 3 : 44E15C 0000
> 5 : 44E15C 0000
> 5 : 44E15C 0000
> 
> Now what would it mean if it were to output :
> Same Value.
> 3 : 5B536C 59D020
> 3 : 59CE0C 59CEF0
> 5 : 5B536C 59D020
> 5 : 59CE0C 59CEF0
> (Output from essentially the same piece of code within a larger project)
> 
> Not the same object, but still able to change it with one call.
> What is it I don't get?
> 
> ------
> module main;
> 
> import std.stdio;
> import std.string;
> 
> interface I{
> 	char[] toString();
> 	int value();
> 	void value(int v);
> }
> 
> class C : I{
> 	private int _value;
> 	
> 	this(int v){ _value = v; }
> 	char[] toString(){ return format(_value); };
> 	int value(){ return _value; };
> 	void value(int v){ _value = v; };
> }
> private I[3][3] arr;
> 
> public I getI( int x, int y){ return arr[x][y]; }
> public void setI( int x, int y, I i ){ arr[x][y]= i; }
> 
> void main(){
> 	C c = new C(3);
> 	setI( 0, 0, c );
> 	setI( 1, 2, c );
> 	I i1 = null;
> 	I i2 = null;
> 	i1 = getI(0,0);
> 	i2 = getI(1,2);
> 	
> 	if( i1 !is null && i2 !is null && i2.value == i1.value ) {
> 		writefln("Same Value.");
> 		if( i2 is i1 ) writefln("Same Object.");
> 		writefln( i2.toString()," : ",i2.__vptr," ",i2.__monitor);
> 		writefln( i1.toString(), " : ", i1.__vptr," ",i1.__monitor);
> 		i1.value = 5;
> 		writefln( i2.toString()," : ",i2.__vptr," ",i2.__monitor);
> 		writefln( i1.toString(), " : ", i1.__vptr," ",i1.__monitor);
> 	}
> }

The code works as expected with 2.042

I had to modify the toString() functions to return string, and say 
"override" in C's toString definition; and had to modify the writefln() 
calls:

   writefln("%s : %s %s", i2.toString(), i2.__vptr, i2.__monitor);

The output:

Same Value.
Same Object.
3 : 806D3F4 0
3 : 806D3F4 0
5 : 806D3F4 0
5 : 806D3F4 0

Ali