The following sample illustrates the class interface definition file (IDL):

//# CLASS: Stack
//#
//# CLASS HIERARCHY:
//#
//#    SOMObject
//#      ÀÄÄÄWPObject
//#            ÀÄÄÄWPAbstract
//#                  ÀÄÄÄStack
//#

#ifndef wpstack_idl
#define wpstack_idl

#include "wpabs.idl"
typedef somToken PSTACKENTRY;  //# Dummy typedef for instance variable

interface M_Stack;

interface Stack : WPAbstract
{
  ULONG InsertStackPage(in HWND hwndDlg);
  //# PARAMETERS:
  //#   HWND  hwndDlg   // In -  notebook dialog window handle
  //#   ULONG return    // Out - 0 = error occurred, else page #
  //#
  //# DESC: Adds the new Settings notebook page.

  BOOL Lock();
  //# PARAMETERS:
  //#   BOOL  return  // Out - TRUE  = successful
  //#                          FALSE = errror
  //#
  //# DESC: Lock the stack using a mutex semaphore so we don't have
  //#       to worry about multiple threads messing up the linked list.

  BOOL Pop(in PVOID pBuffer, inout ULONG pcbBuffer);
  //# PARAMETERS:
  //#   PVOID pBuffer,      // In    - pointer to buffer for popped item
  //#   PULONG pcbBuffer);  // InOut - size in bytes of pop buffer (in),
  //#                       //         size actually returned (out)
  //#   BOOL  return        // Out   - TRUE  = successful
  //#                                  FALSE = errror
  //# DESC: Pops an entry from the stack.

  BOOL Push(in PVOID pNewItem, in ULONG cbNewItem);
  //# PARAMETERS:
  //#   PVOID pNewItem,   // In  - pointer to the item to push
  //#   ULONG cbNewItem   // In  - size in bytes of item to push
  //#   BOOL  return      // Out - TRUE  = successful
  //#                              FALSE = errror
  //# DESC: Pushes an entry onto the stack.

  BOOL Unlock();
  //# PARAMETERS:
  //#   BOOL  return  // Out - TRUE  = successful
  //#                          FALSE = errror
  //#
  //# DESC: Unlock the stack, releasing the mutex semaphore.

  #ifdef __SOMIDL__
  implementation
  {
    releaseorder: InsertStackPage, Lock, Pop, Push, Unlock;

    /*
     * Class modifiers
     */
    functionprefix = stk_;
    majorversion   = 1;
    minorversion   = 2;
    filestem       = wpstack;
    metaclass      = M_Stack;
    callstyle      = oidl;
    dllname        = "wpstack.dll";

    /*
     * Internal instance variables
     */
    BOOL        bInitialized;
    PSTACKENTRY pStackTop;
    HMTX        hmtxStack;

    /*
     * Passthru to the .IH file the following:
     */
    passthru C_ih =
    "#define STK_APPLICATION        \"wpstack class\""
    "#define STK_PERSISTENTCOUNTKEY \"object count\""
    "#define MPNULL                 (MPFROMP( NULL ))"
    "#define MPZERO                 (MPFROMSHORT( 0 ))"
    "#define MRTRUE                 (MRFROMSHORT( (SHORT) TRUE ))"
    "#define MRFALSE                (MRFROMSHORT( (SHORT) FALSE ))"
    ""
    "typedef struct _STACKENTRY"
    "{"
    "   struct _STACKENTRY *Next;"
    "   BYTE        ReserveZeros[8];"
    "   ULONG       cbEntry;"
    "   BYTE        Entry[1];"
    "} STACKENTRY, *PSTACKENTRY;"
    "";

    /*
     * Passthru to the .H file the following:
     */
    passthru C_h =
    "#define STK_AWAKECOUNT      1"
    "#define STK_PERSISTENTCOUNT 2"
    "";

    /*
     * Method modifiers
     */
    wpAddSettingsPages:              override;
    wpFree:                          override;
    wpInitData:                      override;
    wpObjectReady:                   override;
    wpRestoreState:                  override;
    wpSaveState:                     override;
    wpSetup:                         override;
    wpSetupOnce:                     override;
    wpUnInitData:                    override;
  };
  #Endif /* __SOMIDL__ */
};

interface M_Stack : M_WPAbstract
{
  ULONG clsDecObjectCount(in ULONG ulCountType);
  //# PARAMETERS:
  //#   ULONG ulCountType  // In  - STK_AWAKECOUNT,
  //#                               STK_PERSISTENTCOUNT
  //#   ULONG return       // Out - new count value
  //#
  //# DESC: Decrements the number of defined object instances.

  ULONG clsIncObjectCount(in ULONG ulCountType);
  //# PARAMETERS:
  //#   ULONG ulCountType  // In  - STK_AWAKECOUNT,
  //#                               STK_PERSISTENTCOUNT
  //#   ULONG return       // Out - new count value
  //#
  //# DESC: Increments the number of defined object instances.

  HMODULE clsQueryModuleHandle();
  //# PARAMETERS: HMODULE return // Out - DLL module handle
  //#
  //# DESC: Gets resource module handle.

  ULONG clsQueryObjectCount(in ULONG ulCountType);
  //# PARAMETERS:
  //#   ULONG ulCountType  // In  - STK_AWAKECOUNT,
  //#                               STK_PERSISTENTCOUNT
  //#   ULONG return       // Out - count of awake/persistent instances
  //#
  //# DESC: Returns the current number of defined object instances.

  #ifdef __SOMIDL__
  implementation
  {
    releaseorder: clsDecObjectCount,
                  clsIncObjectCount,
                  clsQueryModuleHandle,
                  clsQueryObjectCount;

    /*
     * Class modifiers
     */
    functionprefix = stkM_;
    majorversion   = 1;
    minorversion   = 2;
    filestem       = wpstack;
    callstyle      = oidl;
    dllname        = "wpstack.dll";

    /*
     * Internal instance variables
     */
    HMODULE  hmod;              /* Resource module handle            */
    ULONG    ulAwakeCount;      /* No. of stack instances in memory  */
    ULONG    ulPersistentCount; /* Total number of stack instances   */

    /*
     * Method modifiers
     */
    wpclsInitData:                   override;
    wpclsQueryDefaultHelp:           override;
    wpclsQueryDefaultView:           override;
    wpclsQueryIconData:              override;
  };
  #Endif /* __SOMIDL__ */
};
#Endif  /* wpstack_idl */