Which data type category is String

Question

As I understand, there are the 2 different ways to categorize data types in VBA.

• Object type vs. Non-Object
• Value type vs. Reference type

I would assume that object types are the same as reference types. But I read that there is a difference regarding assignment between object and non-object types:

Dim i As Integer
i = 1

Dim chrt As Chart
Set chrt = something

Notice the "Set". Now in the following link, String is categorized as reference type.

http://msdn.microsoft.com/en-us/library/t63sy5hs.aspx

But

Dim str As String
Set str = "abc"

is wrong and

Dim str As String
str = "abc"

is correct. Thus reference type and object type is not equivalent. What is the difference?

Answer 1

Your MSDN link is referring to Visual Studio 2013 (.NET), where String is indeed an object (like everything in the .net framework).

VBA strings are values, not objects.

As I understand, there are the 2 different ways to categorize data types in VBA.

• Object type vs. Non-Object
• Value type vs. Reference type

It's simpler than that. An object type is a reference type, and a non-object type is a value type.

In VBA object references are assigned using the Set keyword; in the past, values used to be assigned using the Let keyword (I believe that still works, for compatibility reasons); that's why property setters use Let for value types, as in Public Property Let Foo(value As Integer), and Set for reference types, as in Public Property Set Foo(value As Object).

The language evolved and the Let keyword was eventually dropped for value assignations; Set remained required, for object reference assignations.

But in VBA a String is a value, like an Integer or a Boolean.

Answer 2

VBA does have Value Types and Reference Types, but neither Strings nor Arrays fall neatly into either category.

It's informative to look at the definitions of Value types and Reference Types:

Value Type

• A data type is a value type if it holds the data within its own memory allocation.

Reference Type

• A reference type contains a pointer to another memory location that holds the data.

All Objects use pointers, so they are all Reference Types, while the following store their value at their memory location, so they are all Value Types:

• Boolean
• Byte
• Integer
• Long
• Single
• Double
• Date
• Currency

But Strings and Arrays are different. They do use pointers, so technically they are Reference Types, but the VBA language semantically treats Strings and Arrays as Value Types.

As such, when working with Strings and Arrays, VBA has the following behaviors:

• It is not necessary to use the Set keyword when assigning to a String or Array (unless you're assigning to a member of an Array of objects).

• Assigning the value of one String or Array to another creates a copy of the value.

• The equality operator for comparing Strings is the = operator.