Visual Basic 2012 Programmer's Reference

STRUCTURE INSTANTIATION DETAILS

Structures handle instantiation somewhat differently from object references. When you declare a reference variable, Visual Basic does not automatically allocate the object to which the variable points. In contrast, when you declare a value type such as a structure, Visual Basic automatically allocates space for the variable’s data. That means you never need to use the New keyword to instantiate a structure.

However, the Visual Basic compiler warns you if you do not explicitly initialize a structure variable before using it. To satisfy the compiler, you can use the New keyword to initialize the variable when you declare it.

A structure can also provide constructors, and you can use those constructors to initialize the structure. The following code defines the SPerson structure and gives it a constructor that takes two parameters, the second optional:

Public Structure SPerson
    Public FirstName As String
    Public LastName As String
 
    Public Sub New(
     ByVal first_name As String,
     Optional ByVal last_name As String = "<unknown>")
        FirstName = first_name
        LastName = last_name
    End Sub
End Structure

To use a structure’s constructor, you initialize the structure with the New keyword much as you initialize a reference variable. The following code allocates an SPerson structure variable using the two-parameter constructor:

Dim artist As New SPerson("Sergio", "Aragones")

You can also use structure constructors later to reinitialize a variable or set its values, as shown ...