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Class inheritance, what am i missing?

peri_a

I run into a problem while writing a series of classes inheriting from each other.

i stripped the code to the basic example below for simplicity.

Basically i have a series of classes inheriting from each other in cascade (called MyBaseClass, MyDerivedClass, MyDoubleDerived)and they differ for the value assigned to the F_Type property (value 1 2 and 3 respectively). i am creating an instance of MyDoubleDerived Class assigning it to a variable (and also storing into an Associative array where i can get to it by its ID).

I see that during instantiation the F_Type is correclty set to 3 as well as when i try to reach the property from the object itself.

However when i am inside a method the value of this:F_Type or F_Type is for some reason 2 (but if i am accessing from the associative array storing the object the value is correctly 3). Weird enough the method is defined on the Base class (that has the F_Type= 1 so i cannot understand why the value is 2. could this be a bug of some type? (i see this both in JMP 17.1.0 and JMP 18 Early release, I do not have earlier version available to test)

If(!Namespace Exists( "MyNameSp" ),
	NS=New Namespace( "MyNameSp" );
);

MyNameSp:ARList=associative array(); // i store here the object that i can access via its key for convenience
<BR />// below the fucntion to instantiate the object from the class
MyNameSp:CreateNewObj=Function({ClassName, NewKey},
{Default Local},
	
	ObjRef=NewObject(ClassName,{NewKey});
	show(ObjRef:ObjID);
	MyNameSp:ARList[ObjRef:ObjID]=ObjRef;
	return(ObjRef);
);


Define Class( "MyBaseClass",
	
	F_Type=1;
	ObjID="";
	
	_init_=Method({NewKey},
		this:ObjID=NewKey;
		show("value during initialization");
		show(this:F_Type);
		show(F_Type);
	);


	MyMethod=Method({},
		show("value in method");
		show(F_Type);
		show(this:F_Type);
		show(this:ObjID);
		show(MyNameSp:ARList[this:ObjID]:F_Type);
	);
);

Define Class( "MyDerivedClass",
	baseclass( MyBaseClass ),
	F_Type=2;
);

////////////////////////////////////////////////////////////////////////////
Define Class( "MyDoubleDerived",
	baseclass( MyDerivedClass ),
	F_Type=3;	
);
<BR />// start of the actual script
SampleObj=MyNameSp:CreateNewObj("MyDoubleDerived","Key1");
show("value From script");
show(SampleObj:F_Type);


SampleObj:MyMethod();

Accepted answers

All comments

Craige_Hales

Start with How to use Define Class

I have not used classes in a while, but I'm pretty certain that you don't want to respecify the F_Type variable as part of the subclass definition; you should be setting it in the subclass _init_ method.

Craige_Hales

This is probably closer to what you want

If(!Namespace Exists( "MyNameSp" ),
	NS=New Namespace( "MyNameSp" );
);

MyNameSp:ARList=associative array(); // i store here the object that i can access via its key for convenience
// below the fucntion to instantiate the object from the class
MyNameSp:CreateNewObj=Function({ClassName, NewKey},
{Default Local},
	
	ObjRef=NewObject(ClassName,{NewKey});
	show(ObjRef:ObjID);
	MyNameSp:ARList[ObjRef:ObjID]=ObjRef;
	return(ObjRef);
);


Define Class( "MyBaseClass",
	
	F_Type=1;
	ObjID="";
	
	_init_=Method({NewKey},
		this:ObjID=NewKey;
		show("value during initialization");
		show(this:F_Type);
		show(F_Type);
	);


	MyMethod=Method({},
		show("value in method");
		show(F_Type);
		show(this:F_Type);
		show(this:ObjID);
		show(MyNameSp:ARList[this:ObjID]:F_Type);
	);
);

Define Class( "MyDerivedClass",
	baseclass( MyBaseClass ),
//	F_Type=2;
	_init_=Method({NewKey},
		super:_init_(NewKey);
		F_Type=2;
		show("MyDerivedClass",F_Type);
	);
);

////////////////////////////////////////////////////////////////////////////
Define Class( "MyDoubleDerived",
	baseclass( MyDerivedClass ),
//	F_Type=3;	
	_init_=Method({NewKey},
		super:_init_(NewKey);
		F_Type=3;
		show("MyDoubleDerived",F_Type);
	);

);
// start of the actual script
SampleObj=MyNameSp:CreateNewObj("MyDoubleDerived","Key1");
show("value From script");
show(SampleObj:F_Type);


SampleObj:MyMethod();

"value during initialization";
this:F_Type = 1;
F_Type = 1;
// above, the base class is constructed (at beginning of intermediate)
"MyDerivedClass";
F_Type = 2;
// above, the intermediate class is constructed (at the beginning of most derived)
"MyDoubleDerived";
F_Type = 3;
// above, the most derived class is constructed
ObjRef:ObjID = "Key1";
"value From script";
// below: there is really only one variable F_Type, belonging to the base class
SampleObj:F_Type = 3;
"value in method";
F_Type = 3;
this:F_Type = 3;
this:ObjID = "Key1";
MyNameSp:ARList[this:ObjID]:F_Type = 3;

the derived classes use super:_init_ to make sure their base class is fully constructed, then continue on to initialize the derived class. Redefining the F_Type at each layer is hiding the base class F_Type, not replacing it. I don't understand why your example shows F_Type=2 instead of F_Type=1 inside the method call, but the problem goes away with the usage pattern above.

peri_a

Thanks for the reply.

While readapting the code is easy enough that i can continue working i am not really understanding what is behind the curtains.

when i am calling the properties directly it gets the right value (3), it is only from within the method that the value is 2 (and not 1) i also tried to add another level (and is always the n-1 level that is considered).

Additionally this raises another question what about inheritance of methods that are also stored in variables... should i also define the specific methods from within the"_init_"?.

peri_a

I double checked and the same behavior is true also for methods.

if you call a specific method from another a method and the "target" method differs in the different level of inheritance, the method of the "one level up" class in the stack is used (not sure the wording makes sense).

similarly if i define the method of the derived class from within "_init_" method all works as expected

While for variable i can understand the logic of doing in the "_init_" method, for the methods seems counter intuitive.

Is there any documentation on it?

here the modified example:

If(!Namespace Exists( "MyNameSp" ),
	NS=New Namespace( "MyNameSp" );
);

MyNameSp:ARList=associative array();

MyNameSp:CreateNewObj=Function({ClassName, NewKey},
{Default Local},
	
	ObjRef=NewObject(ClassName,{NewKey});
	show(ObjRef:ObjID);
	MyNameSp:ARList[ObjRef:ObjID]=ObjRef;
	return(ObjRef);
);


Define Class( "MyBaseClass",
	
	F_Type=1;
	K_Type=1;
	ObjID="";
	
	_init_=Method({NewKey},
		this:ObjID=NewKey;
		
		
	);
	
	MyChangeInitMethod=Method({PassedType, passedID},
		show("INIT Base Level method (1) ",PassedType, passedID);
	);
	
	MyMethod=Method({},
		this:MyChangeMethod(this:F_Type,this:ObjID);
		this:MyChangeInitMethod(this:F_Type,this:ObjID);
	);
	
	MyChangeMethod=Method({PassedType, passedID},
		show("Base Level method (1) ",PassedType, passedID);
	);
);

Define Class( "MyDerivedClass",
	baseclass( MyBaseClass ),
	F_Type=2;
	
	_init_=Method({NewKey},
		this:ObjID=NewKey;
		K_Type=2;
		MyChangeInitMethod=Method({PassedType, passedID},
			show("INIT Derived class Method (2)",PassedType, passedID);
		);
	);
	
	MyChangeMethod=Method({PassedType, passedID},
		show("Derived class Method (2)",PassedType, passedID);
	);
);

////////////////////////////////////////////////////////////////////////////
Define Class( "MyDoubleDerived",
	baseclass( MyDerivedClass ),
	F_Type=3;
	
	_init_=Method({NewKey},
		this:ObjID=NewKey;
		K_Type=3;
		MyChangeInitMethod=Method({PassedType, passedID},
			show("INIT double Derived class method (3)",PassedType, passedID);
		);
	);
	MyChangeMethod=Method({PassedType, passedID},
		show("double Derived class method (3)",PassedType, passedID);
	);
);

////////////////////////////////////////////////////////////////////////////
Define Class( "MyTripleDerived",
	baseclass( MyDoubleDerived ),
	F_Type=4;
	
	_init_=Method({NewKey},
		this:ObjID=NewKey;
		K_Type=4;
		MyChangeInitMethod=Method({PassedType, passedID},
			show("INIT Triple Derived class method (4)",PassedType, passedID);
		);
	);
	
	MyChangeMethod=Method({PassedType, passedID},
		show("Triple Derived class method (4)",PassedType, passedID);
	);
);

SampleObj1=MyNameSp:CreateNewObj("MyBaseClass","Key1");
SampleObj2=MyNameSp:CreateNewObj("MyDerivedClass","Key2");
SampleObj3=MyNameSp:CreateNewObj("MyDoubleDerived","Key3");
SampleObj4=MyNameSp:CreateNewObj("MyTripleDerived","Key4");
show("----------------Calling the method via a method-------------------");
show("       1       ");
SampleObj1:MyMethod();
show("       2       ");
SampleObj2:MyMethod();
show("       3       ");
SampleObj3:MyMethod();
show("       4       ");
SampleObj4:MyMethod();
show("----------------Clling the method directly------------------------");
show("       1       ");
SampleObj1:MyChangeMethod(SampleObj1:F_Type,SampleObj1:ObjID);
show("       2       ");
SampleObj2:MyChangeMethod(SampleObj2:F_Type,SampleObj2:ObjID);
show("       3       ");
SampleObj3:MyChangeMethod(SampleObj3:F_Type,SampleObj3:ObjID);
show("       4       ");
SampleObj4:MyChangeMethod(SampleObj4:F_Type,SampleObj4:ObjID);