/* Example from Hansen and Sestoft: C# Precisely */

class C<T> where T: class{
  T f = null;
}

class D<U> where U: struct{
  U? f;
} 

class Appl{

  // Does NOT compile:
  C<double> c = new C<double>();
  D<A>      d = new D<A>();  

  // OK:
  C<A>      c1 = new C<A>();
  D<double> d1 = new D<double>();  
  
} 

class A{}