C#

public abstract class BaseClass
{
}

public class Leaf
{
}

public class LeafA : Leaf
{
}

public class LeafB : Leaf
{
}

public class Composite<TChild> where TChild : BaseClass
{
  private List<TChild> _children = new List<TChild>();
  public List<TChild> Children { get { return _children;}}
}

Composite<BaseClass> root = new Composite<BaseClass>();

root.Children.Add(new LeafB());
root.Children.Add(new LeafA());


Composite<LeafA> comp = new Composite<LeafA>();
comp.Children.Add(new LeafA());
comp.Children.Add(new LeafA());

root.Children.Add(comp);

comp = new Composite<LeafB>();
comp.Children.Add(new LeafB());
comp.Children.Add(new LeafB());

root.Children.Add(comp);

foreach (BaseClass b in root.Children)
{
  // test if Leaf
  if (b is Leaf)
  {
  }
  // else it must be Composite
  else
  {
    Composite<BaseClass> child = (b as Composite<BaseClass>); // child is null after this cast
  }
}

SAMPLEDLL_API void StringAsOUT_AllocatedInDll( char ** szParam )<br />
{<br />
*szParam = new char [ 128 ];<br />
strcpy( *szParam, "Please free my memory after using me!" );<br />
}

class Imports<br />
{<br />
[DllImport("SampleDLL.dll")]<br />
public static extern void StringAsOUT_AllocatedInDll( ref int szParam );<br />
...<br />
}

...<br />
Imports impObj = new Imports();<br />
int iAddressOfANSIString = 0;<br />
impObj.StringAsOUT_AllocatedInDll( ref iAddressOfANSIString );<br />
string strOUTPUTFromUnmanagedDll = Marshal.PtrToStringAnsi( ( IntPtr ) iAddressOfANSIString );<br />
Console.WriteLine( "Value of strOUTPUTFromUnmanagedDll = {0}", strOUTPUTFromUnmanagedDll );<br />
...