Unnamed Default Property - vbscript

Question

In VBScript, some built in objects use an unnamed property. Some Examples:
Set Dict = Server.CreateObject("Scripting.Dictionary")
Set RS = GetEmloyeesRecordSet()
Dict("Beer") = "Tasty" ' Same as Dict.Item("Beer") = "Tasty"
Dict("Crude Oil") = "Gross" ' Same as Dict.Item("Crude Oil") = "Gross"
Response.Write "The First Employee Is: " & RS("Name") ' Same as RS.Fields("Name")
How can I use this same syntax in my own classes?
UPDATE
Here is a working, stand-alone example of how to do this, a simple wrapper for Scripting.Dictionary. Note the use of "Let" to allow the d("key") = "value" syntax. Of course credit goes to Thom for providing the answer.
<%
Class DictWrapper
Private Dict
Private Sub Class_Initialize()
Set Dict = Server.CreateObject("Scripting.Dictionary")
End Sub
Private Sub Class_Terminate()
Set Dict = Nothing
End Sub
Public Property Get Count
Count = Dict.Count
End Property
Public Default Property Get Item( Key )
Item = Dict(Key)
End Property
Public Property Let Item( Key, Value )
Dict(Key) = Value
End Property
Public Sub Add( Key, Value )
Dict.Add Key, Value
End Sub
End Class
Dim d : Set d = New DictWrapper
d.Add "Beer", "Good"
Response.Write d("Beer") & "<br>"
d("Beer") = "Bad"
Response.Write d("Beer")
%>

Answer 1

You need to declare a property of the class as the default property. As an example, here's part of a String wrapper class I wrote:
class StringClass
private finished_
private data_
private size_
public function init (val)
finished_ = cStr(val)
set init = me
end function
public default property get value
if (size_ > 0) then
finished_ = finished_ & join(data_, vbNullString)
data_ = empty
size_ = 0
end if
value = finished_
end property
public property let value (val)
data_ = empty
size_ = empty
init(val)
end property
public function add (s)
size_ = size_ + 1
if (isEmpty(data_)) then
redim data_(MIN_ARRAY_SIZE)
elseif (size_ > uBound(data_)) then
redim preserve data_(Float(uBound(data_) * GRANTED_HEAD_ROOM).ceil)
end if
data_(size_ - 1) = cStr(s)
end function
end class
Usage:
dim s: set s = new StringClass
s()= "Hello, world!" ' s.value() = "Hello, world!"
Response.Write s ' Response.Write s.value()
You can also have a parametrized default property:
class ListClass
private size_
private data_
private sub CLASS_INITIALIZE
size_ = 0
data_ = Array()
resize_array MIN_ARRAY_SIZE
end sub
public default property get data (index)
if isObject(data) then
set data_(index) = data
else
data_(index) = data
end if
end property
public property let data (index, value)
data_(index) = value
end property
public property set data (index, value)
set data_(index) = value
end property
public function add(datum)
size_ = size_ + 1
if (size_ > uBound(data_) + 1) then expand_array
assign data_(size_ - 1), datum
add = datum
end function
end class
dim l: set l = new ListClass
l.add("Hello, world!")
l(0) = "Goodbye, world!"
Response.Write l(0)
This second example is probably what you were looking for, using default properties to implement collections, but it's worth checking out the first example, using default properties to implement auto-unboxing of wrapper classes.