private ConnectToPropertyChanged ( property : string, dataContext : object ) : void
    {
      def propertyChanged = dataContext : INotifyPropertyChanged;
    }

expected System.ComponentModel.INotifyPropertyChanged, got object in type-enforced expression: System.Object is not a subtype of System.ComponentModel.INotifyPropertyChanged [simple require]

def propertyChanged = match (dataContext) { | x is INotifyPropertyChanged => x; | _ => null }

def propertyChanged = match(dataContext)
{
  | x is INotifyPropertyChanged => x
  | _ => null
}

    
V>    private ConnectToPropertyChanged ( property : string, dataContext : object ) : void
V>    {
V>      def propertyChanged = dataContext : INotifyPropertyChanged;
V>    }

V>

private ConnectToPropertyChanged ( property : string, dataContext : object ) : void
{
  match(dataContext)
  {
    | x is INotifyPropertyChanged =>
      x.PropetyChanged += (_, e) =>
      {
         when(e.PropertyName == property)
         {
           ...
         }
      }
    | _ => () // ничего не делаем
  }
}

      def propertyChanged = dataContext : INotifyPropertyChanged;
      when ( propertyChanged != null )
        propertyChanged.PropertyChanged += ( s, e ) => when ( e.PropertyName == property ) PropertyChanged ( s, e.PropertyName );

      try
      {
         def propertyChanged = dataContext :> INotifyPropertyChanged;
         propertyChanged.PropertyChanged += ( s, e ) => when ( e.PropertyName == property ) PropertyChanged ( s, e.PropertyName );
      }
      catch ( e : InvalidCastException )
      {

      }

V>      def propertyChanged = dataContext : INotifyPropertyChanged;
V>      when ( propertyChanged != null )
V>        propertyChanged.PropertyChanged += ( s, e ) => when ( e.PropertyName == property ) PropertyChanged ( s, e.PropertyName );
V>

match (dataContext)
{
  | propertyChanged is INotifyPropertyChanged => 
    propertyChanged.PropertyChanged += ( s, e ) => when ( e.PropertyName == property ) PropertyChanged ( s, e.PropertyName );

  | _ => ()
}