Why is this a compile-time error?

[Patrick Mills]

Using CC 5.01.0100 on Windows Vista.

I'm having a problem getting the compiler to accept a fairly simple compound object reference, of this form:

PrintTree oNode.LeftNode, sOrder
Prototype: SUB PrintTree(BYVAL oNode as iface_Node, BYVAL sOrder AS STRING)

However, the same compound reference (oNode.LeftNode) works with this subroutine prototype:

PrintTree oNode.LeftNode
Prototype: SUB PrintTree(BYVAL oNode as iface_Node)

In the first case, I get a compiler error indicating that "Parameter mismatches definition", but the oNode.LeftNode expression should return a reference to iface_Node, which the subroutine is expecting.

In the second case, as long as I have no additional parameters defined to pass to the subroutine, the same expression compiles (and works) just fine.

Am I doing something wrong? The problem causes me to have to call the PrintTree routine (as defined in case 1 above) as follows:

DIM oLeftNode as iface_Node

oLeftNode = oNode.LeftNode
PrintTree oLeftNode, sOrder

This works, but results in unnecessarily complicated code, and requires an additional object reference to be defined and created.

More complete (pastable) code examples follow:

This code compiles (note: code doesn't do anything - I've removed all code unnecessary to demonstrate any problem except the compile-time exception).

#COMPILE EXE
#DIM ALL

CLASS Node
    INSTANCE pLeftNode AS iface_Node
    INSTANCE pRightNode AS iface_Node
    INSTANCE pValue AS LONG
    
    INTERFACE iface_Node
        INHERIT IUNKNOWN
        
        PROPERTY GET LeftNode AS iface_Node
            PROPERTY = pLeftNode
        END PROPERTY
        
        PROPERTY GET RightNode AS iface_Node
            PROPERTY = pRightNode
        END PROPERTY
        
        PROPERTY GET Value AS LONG
            PROPERTY = pValue
        END PROPERTY
        
    END INTERFACE
    
END CLASS

SUB PrintTree(BYVAL oNode AS iface_Node)
    
    IF ISNOTHING(oNode) THEN EXIT SUB
    PrintTree oNode.LeftNode
    STDOUT FORMAT$(oNode.Value)
    PrintTree oNode.RightNode

END SUB

FUNCTION PBMAIN () AS LONG
    DIM oNode AS iface_Node
    
    PrintTree oNode
    
END FUNCTION

This code does *not* compile:

#COMPILE EXE
#DIM ALL

CLASS Node
    INSTANCE pLeftNode AS iface_Node
    INSTANCE pRightNode AS iface_Node
    INSTANCE pValue AS LONG
    
    INTERFACE iface_Node
        INHERIT IUNKNOWN
        
        PROPERTY GET LeftNode AS iface_Node
            PROPERTY = pLeftNode
        END PROPERTY
        
        PROPERTY GET RightNode AS iface_Node
            PROPERTY = pRightNode
        END PROPERTY
        
        PROPERTY GET Value AS LONG
            PROPERTY = pValue
        END PROPERTY
        
    END INTERFACE
    
END CLASS

SUB PrintTree(BYVAL oNode AS iface_Node, BYVAL sOrder AS STRING)
    DIM i AS LONG
    
    IF ISNOTHING(oNode) THEN EXIT SUB
    
    FOR i = 1 TO LEN(sOrder)
        SELECT CASE MID$(sOrder,i,1)
            CASE "1"
                PrintTree oNode.LeftNode, sOrder
            CASE "2"
                STDOUT FORMAT$(oNode.Value)
            CASE "3"
                PrintTree oNode.RightNode, sOrder
        END SELECT
    NEXT i
END SUB

FUNCTION PBMAIN () AS LONG
    DIM oNode AS iface_Node
    
    PrintTree oNode, "123" 'Print tree in pre-order sequence
    
    PrintTree oNode, "321" 'Print tree in post-order sequence

    PrintTree oNode, "213" 'Print tree in in-order sequence

END FUNCTION