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Object-oriented Programming in C#
Abstract classes, Interfaces, and Patterns
Parameter Variance

How do the parameters of Op in class A and B vary in relation the variation of A and B

Class B is a subclass of class A, and T is a subclass of S.

   A aref;
   B bref = new B();
   S sref = new S();

   aref = bref;    // aref is of static type A and dynamic type B
   aref.Op(sref);  // B.Op is called with an S-object as parameter.
                   // What if an operation from T is activated on the S-object?

An illustration of the problems with covariance.

/user/normark/oop-csharp-1/sources/c-sharp/co-contra-varians/ex.csThe full C# program.

It turns out that parameter variance is not really a relevant topic in C#...