Data Type - Object

This data type contains a reference (or an address) to an actual object.
This can be used to contain any type of object (or Reference Type).
This data type uses 4 bytes.
The default value is Nothing.

Dim myObject As Object 

Avoid This Data Type

Using the generic Object data type is much less efficient than using the specific object declaration.
Whenever you use this data type it will always use late binding.
You can find out if an Object variable has been set by using the "Is Nothing" keywords.
It makes your code less readable.
The reasons for this is because Excel cannot tell what type of object the variable refers to until the program is running, which obviously consumes some execution time.
This is referred to as late binding and can make programs run significantly more slowly.

Late Binding

Using the Object data type will declare the variable using late binding.

Dim oWorkbook As Object 

more details

Early Binding

Dim oWorkbook As Workbook 

more details

Set Keyword

You cannot assign an object to a variable using an equals sign.
Instead you must always use the "Set" statement.

GetObject Function

GetObject - Returns the reference to an object provided by an ActiveX component.
This can be used when you want to access a current instance of an object.
This code adds a new workbook to the current Excel instance.

Dim oXLApp As Excel.Application 
Dim oWbk As Excel.Workbook 
Set oXLApp = GetObject(ThisWorkbook.Name).Application 
Set oWbk = oXLApp.Workbooks.Add 

CreateObject Function

CreateObject - Returns the reference after creating a new ActiveX or OLE Object.
This code can be usedfrom Word to create an instance of Excel using early binding.

Dim oXLApp As Excel.Application 
Dim oWbk As Excel.Workbook 
Set oXLApp = CreateObject("Excel.Application") 
Set oWbk = oXLApp.Workbooks.Add 

Passing Objects In

When you declare a variable with an Object data type it can assigned a value using the Set keyword.

Dim myObject As Object 
Set myObject = ThisWorkbook 

It is possible to pass an object into a subroutine or function

Call PassingIn(myObject) 

Public Sub PassingIn(ByRef myObject As Object) 
   Debug.Print TypeName(myObject) 
   'Workbook
End Sub 

Always By Reference

It doesn't matter if you pass in this variable using ByVal or ByRef, the object is always passed by reference.
This means that a reference pointer is passed in and not a copy of the actual object.

ByRef vs ByVal

There is a difference though between the following 2 lines
Public Sub PassingIn(ByRef myObject As Object)
Public Sub PassingIn(ByVal myObject As Object)
ByRef - Passes in the original reference pointer
ByVal - Passes in a copy of the reference pointer
The object will be modified in both cases
ByRef - Caller variable can be reassigned
ByVal - Caller variable cannot be reassigned

Example

Public Sub Testing() 
   Dim myObject As Object 
   Set myObject = Range("A1") 
   Call PassedByRef(myObject) 
   Debug.Print myObject.Address    '$B$1 - changed  
   myObject.Value = 20 

   Set myObject = Range("A1") 
   Call PassedByRef(myObject) 
   Debug.Print myObject.Address    '$A$1 - unchanged  
   myObject.Value = 20 
End Sub 

Public Sub PassedByRef(ByRef r As Range) 
   Set r = Range("B1") 
End Sub 

Public Sub PassedByVal(ByVal r As Range) 
   Set r = Range("C1") 
End Sub