Cast of a Generic Type in .NET -

why following cast not working ?

public void add<t>() t : myinterface {    var newobject = new factory<t>() factory<myinterface>;     ... }  public class factory<t> t : myinterface  { ... } 

newobjects remains null.

probably because factory<t> not subtype of factory<myinterface>, , cast fails.

factory<t> invariant (assuming it's class), means factory<string> not derive factory<object>, though string derives object.

what you're looking covariance. unfortunately, classes cannot variant in c#, interfaces can, iiiif generic type parameter t used output (e.g., method's return type) , never input (e.g., method parameters).

if factory uses t output, can define covariant inteface such as:

public interface ifactory<out t> {}  public class factory<t> : ifactory<t> {} 

now can cast ifactory<t> t:myinterface ifactory<myinterface>