Moving from VBScript to Visual Basic

You should be aware of quite a few syntactical changes to the Visual Basic programming language before you start any project in this language. This section looks at most of the changes in Visual Basic .NET.

Set

Let’s start out with the keyword Set. In short, it is gone. The standard object instantiation in Visual Basic is shown here:

Set objMyObj = objSomeOtherObj 

In Visual Basic .NET, this code has been shortened to more closely match the C# programming language. The same code in Visual Basic .NET looks like this:

objMyObj = objSomeOtherObj 

Properties

Properties have been greatly simplified in the world of the new Visual Basic. Previously, a series of properties looked like the code in Listing A.7.

Listing A.7. Visual Basic Property Code

Private gsString As String 
Private goObject as Object 

Public Property Let StringProp(ByVal psData as String) 
    gsString = psData 
End Property 

Public Property Get StringProp() As String 
    StringProp = gsString 
End Property 

Public Property Set ObjectProp(ByVal poObj as Object) 
    Set goObject = poObj 
End Property 

In Visual Basic .NET, this is much shorter; an example is given in Listing A .8.

Listing A.8. Visual Basic .NET Property Code

Private gsString as String 
Private goObject as Object 

Public Property StringProp as String 
    Get 
        StringProp = gsString 
    End Get 

    Set 
        gsString = StringProp 
    End Set 
End Property 

As you can see, there is no longer a distinction between a Set and a Let because of the change mentioned in the last section.

Calling Subs

Calls of all types (function, method, and sub) must use parentheses around the parameters, regardless of whether you are doing something with the return value. For example, the code in Listing A .9 would work in Visual Basic or VBScript.

Listing A.9. Visual Basic Function Calls

dtDate = Date 
MyFunction "Value1", 2, plVal 

However, in Visual Basic .NET, you would need to change these same calls to the code shown in Listing A.10.

Listing A.10. Visual Basic .NET Function Calls

dtDate = Date() 
MyFunction("Value1", 2, plVal) 

Parameters

A major change to the ways parameters are passed has been introduced into Visual Basic .NET. Previously, all parameters were passed ByRef if no method was specified. Now, all intrinsic types are passed ByVal. So, the function in Listing A.11 would no longer work in Visual Basic .NET.

Listing A.11. Visual Basic Function with ByRef Parameters

Sub MyFunction(plLng1 As Long, plLng2 As Long, plLng3 As Long) 
    plLng3 = plLng1 + plLng2 
End Sub 

In Visual Basic .NET, this subroutine would have to be rewritten as shown in Listing A.12.

Listing A.12. Visual Basic .NET Function with ByRef Parameters

Sub MyFunction(plLng1 As Long, plLng2 As Long, ByRef plLng3 as Long) 
    plLng3 = plLng1 + plLng2 
End Sub 

Datatypes

Unlike VBScript, Visual Basic supports a wide range of variable types. The same can be said of Visual Basic .NET. In previous server-side code you have written, all variables were declared as type Variant. With your server-side code written in Visual Basic .NET, it is highly recommended that, when you’re declaring variables, you define them appropriately so that they will not use excess memory and will be far more efficient. Listing A.13 shows a few examples of how to declare variables of specific types.

Listing A.13. Visual Basic .NET Variable Declarations

Dim psString As String 
Dim plLong as Long 
Dim bByte as Byte 

Also be aware that the Currency datatype has been removed.

Something else to note is that the sizes of certain intrinsic datatypes have changed. Refer to Table A.2 for more information.

Note here that the sizes for Integer and Long datatypes have changed. Long is now 64 bits instead of 32 bits, and Integer is now 32 bits rather than 16 bits.

Variant

The Variant datatype no longer exists in Visual Basic .NET. It has been replaced with the universal Object type. Also removed from Visual Basic .NET is the VarType function. Now, to get the type of a specific variable, you can use the following property that is a member of all the intrinsic datatypes:

SomeObj.GetType.GetTypeCode.value 

Declarations

A new feature of Visual Basic .NET is the capability to initialize variables and arrays at the time of declaration, as shown in Listing A.14.

Listing A.14. Visual Basic .NET Variable Initializations

Dim psString As String = "Hello!" 
Dim piInt as Integer = 123 
Const cSTRING = "Goodbye!" 
Dim psArray(2) As String = ("Brian", "Jon") 

Note, however, that the capability to declare strings of a predefined length is missing in Visual Basic .NET. Therefore, the statement Dim psString As String * 5 is no longer valid.

Shorthand Syntax

Visual Basic .NET now supports shorthand assignment much like C, C++, and Java. The code in Listing A.15 illustrates a few examples of the shorthand notation.

Listing A.15. Shorthand Assignments in Visual Basic .NET

plVal = 100 
plVal += 10 ' plVal now equals 110 
plVal −= 10 ' plVal now equals 100 
plVal *= 5 ' plVal now equals 500 
plVal /= 5 ' plVal now equals 100 

Error Handling

Although the standard On Error GoTo XXX and On Error Resume Next exist in Visual Basic .NET, you also might want to take advantage of its built-in structured error handling, which is similar to that of languages such as C++ and Java. The code in Listing A.16 shows an example of structured error handling in Visual Basic .NET.

Listing A.16. Structured Error Handling in Visual Basic .NET

Try 
    ' Some code 
Catch 
    ' What to run when an error occurs 
Finally 
    ' Code that always executes after try or catch 
End Try 

Structure Declaration

In Visual Basic, structures were defined using the Type…End Type, as shown in Listing A.17.

Listing A.17. Visual Basic .NET Structure

Type Employee 
    EmpName As String 
    EmpNumber As Long 
    EmpAge As Integer 
End Type 

In the new Visual Basic .NET, this same structure would be declared using the Structure…End Structure keywords, as shown in Listing A.18.

Listing A.18. Visual Basic .NET Structure

Structure Employee 
    EmpName As String 
    EmpNumber As Long 
    EmpAge As Integer 
End Structure 

Variable Scope

The scope of variables in Visual Basic .NET is slightly different from that of Visual Basic. In Visual Basic, the code in Listing A.19 would be valid.

Listing A.19. Variable Scope in Visual Basic .NET

For plCount = 0 to 10 
    Dim plVal as Long 
    plVal = plVal + plCount 
Next 

plVal2 = 2 ^ plVal 

In Visual Basic .NET, however, because the variable plVal is declared inside the For…Next loop, its scope is inside that block. Therefore, it cannot be seen outside the loop in the previous example.

Object Creation

In Visual Basic, the following statement would declare an object and set it to Nothing until it was used. At that point, it would reference a new instance of MyObject.

Dim poObject as New MyObject 

In Visual Basic .NET, however, this statement is actually shorthand for the following:

Dim poObject As MyObject = New MyObject 

In this statement, the object is created and references a new instance of the object.

IsMissing

Ironically, in Visual Basic .NET, IsMissing is, well, missing. This means that all optional parameters to a function must be declared with a default value, as follows:

Sub MySub(Optional psStr = "Default value!") 

Control-of-Flow Statements

Certain control-of-flow tatements have been removed from Visual Basic .NET, including these:

• GoSub

• On…GoSub

• On…GoTo (Error…GoTo is still valid)

A change also has been made to the While loop. Previously, While…Wend was valid; however, now the syntax has changed to While…End While.

And the Rest

To wrap this all up, here is a list of everything that has been removed from the Visual Basic .NET programming language:

• As Any keyword phrase

• Atn function

• Calendar property

• Circle statement

• Currency datatype

• Date function and statement

• Debug.Assert method

• Debug.Print method

• Deftype statements

• DoEvents function

• Empty keyword

• Eqv operator

• GoSub statement

• Imp operator

• Initialize event

• Instancing property

• IsEmpty function

• IsMissing function

• IsNull function

• IsObject function

• Let statement

• Line statement

• LSet statement

• MsgBox function

• Null keyword

• On … GoSub construction

• On … GoTo construction

• Option Base statement

• Option Private Module statement

• Property Get , Property Let, and Property Set statements

• PSet method

• Rnd function

• Round function

• RSet statement

• Scale method

• Set statement

• Sgn function

• Sqr function

• String function

• Terminate event

• Time function and statement

• Type statement

• Variant datatype

• VarType function

• Wend keyword