What VB6 method allows two custom objects of the same type (defined in a class module) to be compared to each other? I think there's an equivalent to Java's compareTo method, but I can't find it anywhere.
+2
A:
If by "compare" you mean "are they the same type?", you can you the TypeName function:
If (object1 <> Nothing) and (object2 <> Nothing) then
If (TypeName(object1) = TypeName(object2)) Then
Debug.Print "object types are the same"
Else
Debug.Print "object types are NOT the same"
End If
End If
If by "compare" you mean "do they reference the same object in memory?", you can use the Is operator:
If (object1 Is object2) Then
Debug.Print "objects references are the same"
Else
Debug.Print "objects references are NOT the same"
End If
raven
2010-06-30 13:22:38
What I mean is that two instances of a class with identical attributes should return true. Naturally, you could compare those attributes manually, but I thought that VB6 had a method that you could define where that would happen automatically.
derekerdmann
2010-06-30 13:40:30
Careful: object1 and object2 could be of different types but currently resolve to Nothing.
onedaywhen
2010-06-30 13:43:21
@onedaywhen: Good catch. I assumed that TypeName returned the type of the object variable even if it was set to "Nothing", but instead it returns "Nothing". That complicates things. I put a check in my example code, but if one of those objects is Nothing, I guess a type comparison isn't possible.
raven
2010-06-30 14:55:43
@derek: After reading the clarification you made in your comments, I now understand that I haven't answered your question. Sorry, I know of no method in VB6 that can do what you wish.
raven
2010-06-30 15:05:47
Hey, don't sweat it. Thanks anyway!
derekerdmann
2010-06-30 15:39:25
+1 There's no way to compare object instances by value. I don't think you can even compare structure instances.
MarkJ
2010-06-30 16:37:45
No way besides serializing to byte array...
wqw
2010-06-30 21:06:14
A:
For others who may be wondering about the same question:
After doing a lot of looking around, it seems like VB6 doesn't have any kind of built-in compareTo or equals methods, like Java does.
I forgot that in Java, compareTo is defined in the java.lang.Comparable interface. Since interfaces are so broken in VB6, even if you wrote your own Comparable interface, you would have to call your object's Comparable_compareTo method unless it was declared as Comparable, which is pointless.
Bottom line: if you want compareTo or equals methods in your VB6 classes, just put them in.
derekerdmann
2010-07-01 01:39:08