Object propert ByRef (GOD DAMN IT)

Why can't I transfer Object properties byref??

Code:

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AddToString Char.ApproachedPCs, Trim(NameIndex)

Sub AddToString(ByRef sString$, WordToAdd$, Optional Devider$ = ",")
    If Len(sString) > 0 Then _
      sString = WordToAdd$ & Devider$ & sString _
      Else sString = WordToAdd$
End Sub

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Well after the code ends Trim(NameIndex) is not added to Char.ApproachedPCs property.

Somone knows why it happens and how to make a property to be passed ByRef?