Visual Basic 2005 in a Nutshell, Third Edition

Type Parameters | 135

Generics

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the standard Stack class methods. This is a little better, since you wouldn’t

have to recode the entire Stack logic. But you would still have to do it again

for

String data. And all of this wrapping and type-casting between System.

Object and

Integer can’t be that efficient.

• Just use the existing Stack class and hope that only integers are used. Unfor-

tunately, this doesn’t really solve the problem.

Generics solve this problem by allowing an instance of a class to look like it was

written just for a restricted data type. All enforcement occurs at compile time, so

the program is also more efficient, since the data does not have to be converted to

System.Object and back again all the time. Visual Studio also uses the generic defi-

nitions to enhance the IntelliSense available when working with generics-enabled

types.

Generics are similar to a feature called templates in the C++ language, although

generics are somewhat easier to use and do not support all of the features avail-

able with templates.

Type Parameters

Consider the following subset of the Stack class definition.

Public Class StackSubset

Public Sub Push(ByVal obj As System.Object)

End Sub

End Class

To define this same class using generics, use the new Of keyword.

Public Class StackSubset(Of T)

Public ...