How do I declare a constant variable with a value of a function call - vba

Question

In a VBA module I have the following declaration of constants:
Private Const const_abc = 3000
Private Const const_def = 900
Private Const const_etc = 42
' and so on and so forth
Now, I have to initialize these values with a one time function call, ideally something like so
Private Const const_abc = someFunc(18)
Private Const const_def = someFunc( 7)
Private Const const_etc = someFunc( 5)
' and so on and so forth
Of course, this won't work in VBA. So, is there a common pattern on how to deal with such a requirement?
I probably could go like so
Private const_abc As Double
Private const_def As Double
Private const_etc As Double
sub initConsts()
const_abc = someFunc(18)
const_def = someFunc( 7)
const_etc = someFunc( 5)
end sub
But then I'd have to make sure that initConsts is called which I'd rather not do.
Edit As per the question of S O, I am using MS-Access.

Answer 1

Create a class that reads the cell and presents a Get-only interface to the value.
Here's a class called ItsMyValueClass
Option Explicit
Private pMyVal As Integer
Public Property Get MyValue() As Integer
MyValue = pMyVal
End Property
Private Sub class_initialize()
'pMyVal = Sheet.Range("somewhere)
pMyVal = 17
End Sub
And here's the code in your module:
Option Explicit
Sub IsItReadOnly()
Dim valu As ItsMyValueClass
Dim x As Integer
Set valu = New ItsMyValueClass
x = valu.MyValue
'valu.MyValue = 23 'compile error "Can't assign to read-only property"
End Sub

Answer 2

Public Function White() as Long
White = RGB(255,255,255)
End function
Private Sub TestIt()
Debug.Print "White is " & White
White = 123 ' <-- compile error
End Sub

Answer 3

in a one-liner that works with modules and classes alike for pure constant-like access:
Public Property Get myConst() As Integer: myConst = 3: End Property
you would use it like this:
Sub test()
Debug.Print "myConst: " & myConst 'would print: "myConst: 3"
End Sub
and if it has to be initialized with a custom value once, one could do it with a static property and one or many private variables:
Private ci As Boolean 'constants initialized
Private myConst1_ As Integer
Private myConst2_ As Integer
Static Property Get myConst1() As Integer
If Not ci Then init
myConst1 = myConst1_
End Property
Static Property Get myConst2() As Integer
If Not ci Then init
myConst2 = myConst2_
End Property
Private Sub init()
'these can come from anywhere:
myConst1_ = 3
myConst2_ = 5
ci = True
End Sub
they are initialized on the first access of the first "constant" property
if you have to initialize them earlier one could just call the init function earlier (and optionally remove the ci variable and all related lines if it is ensured that the properties are not accessed earlier)