Csharp/CSharp Tutorial/Generic/Generic Parameter

Create relationship between two type parameters

using System; 
 
class A { 
} 
 
class B : A { 
} 
 
// Here, V must inherit T. 
class Gen<T, V> where V : T {  
} 
 
class MainClass { 
  public static void Main() { 
    Gen<A, B> x = new Gen<A, B>(); 
 
    // error 
    // Gen<B, A> y = new Gen<B, A>(); 
 
  } 
}

Default generic parameter value

using System;
public class Bag<T>
{
    public Bag() {
        // Create initial capacity.
        imp = new T[ 4 ];
        for( int i = 0; i < imp.Length; ++i ) {
            imp[i] = default(T);
        }
    }
    public bool IsNull( int i ) {
        if( i < 0 || i >= imp.Length ) {
            throw new ArgumentOutOfRangeException();
        }
        if( Object.Equals(imp[i], default(T)) ) {
            return true;
        } else {
            return false;
        }
    }
    private T[] imp;
}
public class MainClass
{
    static void Main() {
        Bag<int> intBag = new Bag<int>();
        Bag<object> objBag = new Bag<object>();
        Console.WriteLine( intBag.IsNull(0) );
        Console.WriteLine( objBag.IsNull(0) );
    }
}

True
True