Compiler Warning (level 1) CS0197

Passing 'argument' as ref or out or taking its address may cause a runtime exception because it is a field of a marshal-by-reference class

Any class that derives, directly or indirectly, from MarshalByRefObject is a marshal-by-reference class. Such a class can be marshaled by reference across process and machine boundaries. Thus, instances of this class could be proxies to remote objects. You cannot pass a field of a proxy object as ref or out. So, you cannot pass fields of such a class as ref or out, unless the instance is this, which can not be a proxy object.

Example

The following sample generates CS0197.

// CS0197.cs  
// compile with: /W:1  
class X : System.MarshalByRefObject  
{  
   public int i;  
}  
  
class M  
{  
   public int i;  
   static void AddSeventeen(ref int i)  
   {  
      i += 17;  
   }  
  
   static void Main()  
   {  
      X x = new X();  
      x.i = 12;  
      AddSeventeen(ref x.i);   // CS0197  
  
      // OK  
      M m = new M();  
      m.i = 12;  
      AddSeventeen(ref m.i);  
   }  
}