DevTut

# Generics

# Create a generic class

A generic type is created to adapt so that the same functionallity can be accessible for different data types.

Public Class SomeClass(Of T)
    Public Sub doSomething(newItem As T)
        Dim tempItem As T
        ' Insert code that processes an item of data type t.
    End Sub
End Class

# Instance of a Generic Class

By creating an instance of the same class with a different type given, the interface of the class changes depending on the given type.

Dim theStringClass As New SomeClass(Of String)
Dim theIntegerClass As New SomeClass(Of Integer)

enter image description here (opens new window)

# Define a 'generic' class

A generic class is a class who adapts to a later-given type so that the same functionality can be offered to different types.

In this basic example a generic class is created. It has a sub who uses the generic type T. While programming this class, we don't know the type of T. In this case T has all the characteristics of Object.

Public Class SomeClass(Of T)
    Public Sub doSomething(newItem As T)
        Dim tempItem As T
        ' Insert code that processes an item of data type t.
    End Sub
End Class

# Use a generic class

In this example there are 2 instances created of the SomeClass Class. Depending on the type given the 2 instances have a different interface:

Dim theStringClass As New SomeClass(Of String)
Dim theIntegerClass As New SomeClass(Of Integer)

enter image description here (opens new window) enter image description here (opens new window)

The most famous generic class is List(of )

# Limit the possible types given

The possible types passed to a new instance of SomeClass must inherit SomeBaseClass. This can also be an interface. The characteristics of SomeBaseClass are accessible within this class definition.

Public Class SomeClass(Of T As SomeBaseClass)
    Public Sub DoSomething(newItem As T)
        newItem.DoSomethingElse()
        ' Insert code that processes an item of data type t.
    End Sub
End Class

Public Class SomeBaseClass
    Public Sub DoSomethingElse()
    End Sub
End Class

# Create a new instance of the given type

Creating a new intance of a generic type can be done/checed at compile time.

Public Class SomeClass(Of T As {New})
    Public Function GetInstance() As T
        Return New T
    End Function
End Class

Or with limited types:

Public Class SomeClass(Of T As {New, SomeBaseClass})
    Public Function GetInstance() As T
        Return New T
    End Function
End Class

Public Class SomeBaseClass
End Class

The baseClass (if none given it is Object) must have a parameter less constructor.

This can also be done at runtime through reflection (opens new window)

← Disposable objects →