Visual Basic 2005 in a Nutshell, Third Edition

Nested Generic Types | 139

Generics

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MsgBox(theText.ToUpper( ))

End Sub

End Class

Even if you create an instance of this class with a String:

Dim usingStringNow As UsuallyString(Of String)

the original class definition will not compile because the compiler does not know

in advance that you plan to use it with

String data.

If you place an interface type constraint on a type parameter, uses of that type

parameter can access the members of the interface, as shown in the following

code.

Public Interface ISimple

Sub WriteThisCode( )

End Interface

Public Class UsesISimple(Of T As ISimple)

Public Sub DoTheWork(ByVal theData As T)

' ----- Uses the class-specific implementation.

theData.WriteThisCode( )

End Sub

End Class

If you have multiple type constraints on a type parameter, uses of that parameter

can generally access all members of all type constraints. If name conflicts do exist

between two constraints (such as a class and interface having a member of the

same name), your code will have to cast or convert the typed object to the desired

class or interface (using

CType or some other method) before calling the conflicting

member.

Generic Methods

Type members (functions and sub procedures) can also be defined with type

parameters, whether or not the class in which they appear uses generics. The type ...