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maxValue = value
End If
Next
Console。WriteLine（〃Maximum value is （〃 & maxValue & 〃）〃）
Another variation is as follows：
Dim elements As IList（Of Integer） = New List（Of Integer）（）
elements。Add（1）
elements。Add（2）
elements。Add（3）
Dim runningTotal As Integer = 0
Dim maxValue As Integer = Integer。MinValue
For Each value As Integer In elements
If value 》 maxValue Then
maxValue = value
End If
runningTotal = runningTotal ＋ value
Next
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C HA P TE R 9 ■ L E AR N I N G A B O U T L I ST S； DE L E G AT E S ； AN D L A M B D A E X PR E SSI O N S 237
For one or two instances； writing the For Each loop is not that problematic； but it would be
if you needed to use the iterator code in a dozen places。 This type of code is harder to maintain
and extend。 One way of being more efficient is to delegate the code to an abstract base class
that is implemented to calculate the running total or maximum value。 The following is the
plete code （you can place the three classes in separate files called IteratorBaseClass。vb；
RunningTotal。vb； and MaximumValue。vb if you want to test this）。
MustInherit Class IteratorBaseClass
Protected Sub New（ByVal collection As IList（Of Integer））
_collection = collection
End Sub
Public Function Iterate（） As IteratorBaseClass
Dim element As Integer
For Each element In Me。_collection
ProcessElement（element）
Next
Return Me
End Function
Protected MustOverride Sub ProcessElement（ByVal value As Integer）
Private _collection As IList（Of Integer）
End Class
Class RunningTotal
Inherits IteratorBaseClass
Public Sub New（ByVal collection As IList（Of Integer））
MyBase。New（collection）
Total = 0
End Sub
Protected Overrides Sub ProcessElement（ByVal value As Integer）
Total = Total ＋ value
End Sub
Public Total As Integer
End Class
Class MaximumValue
Inherits IteratorBaseClass
Public Sub New（ByVal collection As IList（Of Integer））
MyBase。New（collection）
MaxValue = Integer。MinValue
End Sub
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238 CH AP T E R 9 ■ L E A R N IN G AB OU T L I ST S； D E L E G A T E S； A N D L A M B DA E X P R E S SI ON S
Protected Overrides Sub ProcessElement（ByVal value As Integer）
If （value 》 MaxValue） Then
MaxValue = value
End If
End Sub
Public MaxValue As Integer
End Class
Module Module1
Sub Main（）
Dim elements As IList（Of Integer） = New List（Of Integer）（）
elements。Add（1）
elements。Add（2）
elements。Add（3）
Dim runningTotal As Integer = _
TryCast（New RunningTotal（elements）。Iterate（）； RunningTotal）。Total
Dim maximumValue As Integer = _
TryCast（New MaximumValue（elements）。Iterate（）； MaximumValue）。MaxValue
Console。WriteLine（〃RunningTotal （〃 & runningTotal & 〃）〃）
Console。WriteLine（〃Maximum Value （〃 & maximumValue & 〃）〃）
End Sub
End Module
The rewritten code is much longer； even though the bolded code； which represents the
user code； is much shorter。 However； this code still isn’t right。 The code is ill fitting because the
problem that it addresses can be solved using another； simpler technique。 So； in a nutshell； you
can say the problem is that you want to solve a single particular technical problem using an
elegant piece of code that does not include repeated sections that have been copied and pasted。
A better solution is consider the code as two code blocks； and in the following section； you’ll
see how delegates can solve the problem of adding and keeping a running total。
WEIGHING THE ADVANTAGES OF REUSING CODE
Very often； when you write code； the code that performs the task directly is shorter and to the point。 When you
abstract the code and develop general classes； the code will begin to bloat and expand； but the advantage is
that the code can be reused。 So； when is abstracting code worth the effort？
Consider the analogy of building a house。 You are constructing the trusses for the house。 You have a
blueprint that indicates that you need to build 50 trusses。 You could build each of the 50 trusses individually；
or you could build a jig to speed up building the trusses。 And herein lies the problem。 If the trusses can be built
without a jig in 10 hours； and with the jig in 2 hours； you would think building the jig was a good idea。 But not
so fast。 What if building the jig takes 20 hours？ Then the time that you saved by using the jig you lost by
building the jig。
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C HA P TE R 9 ■ L E AR N I N G A B O U T L I ST S； DE L E G AT E S ； AN D L A M B D A E X PR E SSI O N S 239
Software is no different。 Sometimes； even though the code