Dim and ReDim with Option Explicit

[igold]

I was reading a posted question on the Forum, and in this particular post, the OP had pasted the entire code starting with the "Option Explicit" at the top. As I read the code I noticed that the OP had not Dimensioned an Array, but only Re-Dimensioned it. I thought that the code would not compile, but it did. I tested it myself and to my surprise there is no need to initially Dimension an Array, but rather if you ReDimension it, that is sufficient. As an example this code will compile.

Option Explicit

Sub test()
    ReDim arr(1 To 10, 1 To 2)
End Sub

Although I do not have any questions, if anyone wants to comment or provide some insight on this, that would be great.

 

[Kaper]

My comment:

with ReDim the array is not only re-dimentioned but also (if it was not declared before) is also declared.
Option explicit forces declaration of all variables before their first use, and as said redim declares variable (if it was not declared before) so it is fine.

Use of arr before redim will cause an error, but use after that will not.

Invalid with Option explicit

Sub test()
    arr(1, 1) = 0
    ReDim arr(1 To 10, 1 To 2)
End Sub

valid

Sub test()
    ReDim arr(1 To 10, 1 To 2)
    arr(1, 1) = 0
End Sub

similar situation with 1 dimentional variable

Sub test()
    i = 2
    ReDim arr(1 To 10, 1 To 2)
    arr(1, 1) = i
    Dim i As Integer
End Sub

even if i is declared, it is declared after first use, so causes a compiler error if Option Exclicit was used
Moreover, if such a code will be used without option explicit, one will get "duplicate declaration in current scope" error, because i has been automatically declared before first use in assignment (i=2) line (as type variant containing integer data)

 

[igold]

I do understand that it works, but perhaps we should clue Microsoft in as well. The following is a quote from docs.microsoft.com

The ReDim statement is used to size or resize a dynamic array that has already been
formally declared by using a Private, Public, or Dim statement with empty
parentheses (without dimension subscripts). Use the ReDim statement repeatedly to
change the number of elements and dimensions in an array

 

[Kaper]

Well, it's almost a philosophy

But is it a first time M$ declares something to be "rather strict" but then it shows to be "quite relaxed"...


So the above post is about "how do I understand why it works" not an official explanation

And going to yout opening post - rather comment than insight.