[Oberon] Type compatibility of procedures

[Srinivas Nayak]

Dear All,


TYPE
	Class = POINTER TO ClassDesc;
	ClassDesc = RECORD
		x : INTEGER;
		method : PROCEDURE (self: Class; v : INTEGER);
	END;
	
	Subclass = POINTER TO SubclassDesc;
	SubclassDesc = RECORD (ClassDesc)
		y : INTEGER
	END;


VAR
	ptr : Class;
	subPtr : SubClass;


If we have two procedures like this:


PROCEDURE Method (self: Class; v : INTEGER);
BEGIN
	self.x := v
END Method;

PROCEDURE OverridingMethod (self: Subclass; v : INTEGER);
BEGIN
	self.x := v;
	self.y := v
END OverridingMethod;


We can do,


NEW(subPtr); subPtr.method := Method;


Can't we do,


NEW(subPtr); subPtr.method := OverridingMethod; ?


If no, is there any reason why we didn't make
these two procedure types compatible?


PROCEDURE Method (self: Class; v : INTEGER);
PROCEDURE OverridingMethod (self: Subclass; v : INTEGER);



With thanks and best regards,

Yours sincerely,
Srinivas Nayak

Home: http://www.mathmeth.com/sn/
Blog: http://srinivas-nayak.blogspot.in/