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In and Out Generic Modifier

Jun 13 2012 12:49 PM
Hi

Given the following 2 code examples:-

// Covariant interface.
interface ICovariant<out R> { }

// Implementing covariant interface.
class Sample<R> : ICovariant<R> { }

class Program
{
static void Test()
{
ICovariant<Object> iobj = new Sample<Object>();
ICovariant<String> istr = new Sample<String>();

// You can assign istr to iobj because
// the ICovariant interface is covariant.
iobj = istr;
}
}

/ Contravariant interface.
interface IContravariant<in A> { }

// Implementing contravariant interface.
class Sample<A> : IContravariant<A> { }

class Program
{
static void Test()
{
IContravariant<Object> iobj = new Sample<Object>();
IContravariant<String> istr = new Sample<String>();

// You can assign iobj to istr because
// the IContravariant interface is contravariant.
istr = iobj;
}
}

I thought Contravariance was Narrower (string) to Wider (object) and Covariance was Wider (object) to Narrower (string).

With the assignments above it indicates the vice versa?

Regards

Steven



Answers (3)