excel vba - Passing objects to procedures in VBA -

i working on simple tool allow me parse multiple csv files , spit them out onto fresh worksheet "merged" together. here implementation (i've simplified it) , issue:

class a

private variables types property methods accessing variables 

class b

private variables types property methods accessing variables 

class c

private ca classa private cb collection  'collection of classb 

class d - part of problem

private cc collection 'collection of classc 'other member variables , property get/lets  public sub adda(a classa)     if cc.item(a.foo) nothing          dim tempc classc         set tempc = new classc         tempc.a =     end if end sub 

main module - other half of problem

dim cc new classc 'initialize class c, works fine dim tempa classa set tempa = new classa 'set tempa properties cc.adda tempa  'this error 

i've tried passing byval , byref each gives me different errors ("byref argument type mismatch", "invalid procedure or argument", , "object doesn't support property or method"

i have no idea try next, tried parenthesis "thing" supposedly forces parameter either byval or byref, can't remember, yesterday.

thanks.

this line:

tempc.a =  

means "assing a property of tempc object value of default property of a object."
a object apparently doesn't have default property.

what meant probably:

set tempc.a =  

but then, can't access private field a of c class d class. make field public or create public seta() method on c class , call d.