Generics in VB.NET

Saw these cups knocking about recently.

I like the implementation of Generics in VB.NET. When you describe a generic type in C# or Java, and you have a type Database<T> you say a "database of T". VB.NET takes this further, the syntax is just Database(of T).

Generics allow you to resuse a class or a method for multiple types that need the same abstract functionality. A good example is two entities in your system that need to be persisted. The entities have different logic and a different reason to exist but they both need to be saved to a database. In this case you can implement the same functionality twice or reuse one class but allow it to be flexible enough to handle both entities.

I saw the picture of that cup knocking about on Twitter recently then I saw people wearing TShirts at a recent Scott Gu talk on Microsoft Azure. I would like to get my hands on an official one!

	Public MustInherit Class ReadModel
	Public Property Id As Guid
	End Class
	Public Class Appointment
	Inherits ReadModel
	Public Property StartTime As DateTime
	Public Property EndTime As DateTime
	End Class
	Public Class Person
	Inherits ReadModel
	Public Property FirstName As String
	Public Property LastName As String
	End Class
	Public Class Repository
	Private _database As IDictionary(Of Type, IDictionary(Of Guid, ReadModel))
	Public Sub New()
	_database = New Dictionary(Of Type, IDictionary(Of Guid, ReadModel))
	End Sub
	Public Sub Save(Of TReadModel As ReadModel)(readmodel As TReadModel)
	If Not _database.ContainsKey(GetType(TReadModel)) Then
	_database.Add(GetType(TReadModel), New Dictionary(Of Guid, ReadModel))
	End If
	_database(GetType(TReadModel)).Add(readmodel.Id, readmodel)
	End Sub
	Public Function Load(Of TReadModel As ReadModel)(id As Guid) As TReadModel
	Return CType(_database(GetType(TReadModel))(id), TReadModel)
	End Function
	End Class
	<TestClass()>
	Public Class RepositoryTests
	<TestMethod()>
	Public Sub PersonRepositoryTest()
	Dim repo As New Repository
	Dim person1 = New Person() With {.Id = Guid.NewGuid, .FirstName = "Dom", .LastName = "Finn"}
	Dim person2 = New Person() With {.Id = Guid.NewGuid, .FirstName = "Billy", .LastName = "Finn"}
	repo.Save(Of Person)(person1)
	repo.Save(Of Person)(person2)
	Dim person1Loaded = repo.Load(Of Person)(person1.Id)
	Assert.IsNotNull(person1)
	End Sub
	<TestMethod()>
	Public Sub AppointmentRepositoryTest()
	Dim repo As New Repository
	Dim app1 = New Appointment() With {.Id = Guid.NewGuid, .StartTime = New DateTime(2015, 1, 1, 9, 0, 0), .EndTime = New DateTime(2015, 1, 1, 9, 30, 0)}
	Dim app2 = New Appointment() With {.Id = Guid.NewGuid, .StartTime = New DateTime(2015, 1, 2, 9, 0, 0), .EndTime = New DateTime(2015, 1, 2, 9, 30, 0)}
	repo.Save(Of Appointment)(app1)
	repo.Save(Of Appointment)(app2)
	Dim person1Loaded = repo.Load(Of Appointment)(app1.Id)
	Assert.IsNotNull(app1)
	End Sub
	End Class

view raw GenericExample.vb hosted with ❤ by GitHub

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Dom Finn

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