Using a Property Let and Get in a VBScript Class

How to Work with an Object's Properties and VBScript Programming

Jul 26, 2009

A property in a VBScript class is some much more than just a variable. A programmer can add code to the get and let statements that will control the object's operations

Any object oriented programming class, VBScript or otherwise, will have properties and each property will need to be set. For example a class used to represent a person may have:

The properties can be included in a class as simple variables however, in the case of VBScript, a property:

This additional functionality can be used to run rules on the information being assigned to the class, for example:

A Simple VBScript Class

The simplest VBScript will simply define each of the properties as a public variable:

Class Person

public age

public gender

public first_name

public surname

public prefix

public marital_status

End Class

Set person_1 as New Person

person_1.gender = "male"

person_1.prefix = "Mr"

However that be automated by using the VBScript property let and get statements.

Using the VBScript Property Let Statement

The Property Let statement is used to define the actions that occur when a value is assigned to the property. So, for example, the class may contains some private variables:

Class Person

Private my_age

Private my_gender

Private my_first_name

Private my_surname

Private my_marital_status

Private my_prefix

The programmer can then update these by creating a property let subroutine, for example:

Public Property Let gender (new_gender)

my_gender = new_gender

If my_gender = "male" Then

my_prefix = "Mr"

Else

Select Case my_marital_status

Case "married"

my_prefix = "Mrs"

Case "unmarried"

my_prefix = "Miss"

Case Else

my_prefix = "Ms"

End Select

End If

End Property

This means, of course, that all of the functionality is built into the class rather than the application that uses the class.

Using the VBScript Property Get Statement

The get statement is used to retrieve the value of the property. However, just the like the let statement, it can have additional functionality built into it. Unlike the let statement it does not need an input. For example, it is useful for setting default values:

Public Property Get prefix

If my_prefix = "" Then

prefix = "unknown"

Else

prefix = my_prefix

End If

End Property

End Class

Public Property Get gender

If my_gender = "" Then

gender = "unknown"

Else

gender = my_gender

End If

End Property

Of course, one of the easiest ways to understand the property let and set statements is to see them in action.

Using the VBScript Get and Let Statements Together

Once all of the property let and get procedures have been set then the class itself starts to become quite intelligent:

Set person_1 = New Person

person_1.gender = "male"

Wscript.echo "Person 1 is a " & person_1.prefix & " and " & person_1.gender

Set person_2 = New Person

person_2.gender = "female"

Wscript.echo "Person 2 is a " & person_2.prefix & " and " & person_2.gender

The result (as shown in figure 1) is that the new object can work out the correct prefix according to the information that is given to it. And that, of course, is the key to object oriented programming: any decision making should be done by the class and not the program using the class. In that way a class will always operate in the same way regardless of where it is used.

The copyright of the article Using a Property Let and Get in a VBScript Class in Windows Programming is owned by Mark Alexander Bain. Permission to republish Using a Property Let and Get in a VBScript Class in print or online must be granted by the author in writing.