Classes and Structures in Visual Basic

Understanding Types

VB.NET provides two primary ways to define complex data structures: classes (reference types) and structures (value types). Choose a class when you need inheritance, polymorphism, or large immutable objects. Use a structure for small, immutable data that benefits from stack allocation.

Show Example ►

Public Class Person
    Public Property FirstName As String
    Public Property LastName As String

    Public Sub New(first As String, last As String)
        Me.FirstName = first
        Me.LastName = last
    End Sub

    Public Function FullName() As String
        Return $"{FirstName} {LastName}"
    End Function
End Class

Public Structure Point
    Public X As Integer
    Public Y As Integer

    Public Sub New(x As Integer, y As Integer)
        Me.X = x
        Me.Y = y
    End Sub
End Structure

Key Differences

Aspect	Class	Structure
Memory Allocation	Heap (reference type)	Stack (value type)
Inheritance	Supports inheritance	No inheritance (except interfaces)
Default Constructor	Can define none; compiler provides one	Must have parameterless constructor automatically
Assignment	Copies reference	Copies entire value
Nullability	Can be Nothing	Cannot be Nothing (except Nullable(Of T))

When to Use a Structure

Data is small (typically < 16 bytes).
Immutability is desired.
Frequent creation and disposal (e.g., points, colors).
No need for inheritance.

When to Use a Class

Complex behavior requiring methods, events, or inheritance.
Object lifetimes managed via garbage collection.
Large data that would be costly to copy.
Polymorphic collections.

Best Practices

Prefer Class for most scenarios.
Make structures immutable: declare ReadOnly fields and provide a constructor.
Implement IEquatable(Of T) for structures to improve equality checks.
Avoid exposing mutable reference fields in structures.