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with two implementations。 If not； use text streams。
o When streaming data； it is best to customize as little as possible。 Doing so will pli
cate your program； and potentially introduce errors where none should exist。
o It is important that you understand the concept of marshaling and the fact that each
medium will have a different representation of the type。 A large part of your programming
day will involve moving data from one stream to another。
Some Things for You to Do
The following are some exercises to apply what you learned in this chapter。
1。 In the implementation of TextProcessor； the display help routine was not very helpful。
Fix the implementation。
2。 There were no testing routines for TextProcessor。 Devise some realistic tests。 By realistic
tests； I mean tests that don’t just focus on the class library and consider the application
tested。 Focus on plete application tests。
3。 Having implemented the display help routine； think about whether or not the imple
mentation is correct。 The class Bootstrap is a general class that uses an IProcessor
instance； which means that different console applications will process different data。
Thus； writing a general help output might work； but it will not help in resolving problems。
Fix the console application TextProcessor and ReaderWriter project so that the help
message is both specific and general。
4。 In the Bootstrap class； when the output was redirected to a file （as indicated by the …out
argument）； there was no check on whether or not the file exists。 Extend the Bootstrap
class to include an additional mand…line argument that verifies if it is fine to overwrite
the output file if it exists。 If an output file does exist and there is no explicit overwriting；
generate an error and stop processing。
5。 The code in the final solution for IProcessor。Process（） has been identified as being hard
to maintain because the code to check for duplicate dates is scattered throughout the
method。 Rewrite the method implementation so that the code is logical and maintainable。
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C H A P T E R 1 1
■ ■ ■
Learning About Generics
Chapter 9 explained how to use lists； delegates； and lambda expressions。 In that chapter； you
also saw an example of generics when using lists to manage a collection of object instances。
The main focus of this chapter is generics and how to use them in a black box context
（the code doesn’t know the specifics of the generics parameter types）。 The secondary
focus is an implementation of lambda expressions using a spreadsheet。 The idea is to get you
well versed in generics and lambda expressions； which you will likely use in your own
production code； so that that there will be no surprises in your projects。
Why Use Generics？
Here’s a surprise for you： there is no imperative need for generics； so you could skip this
chapter and read the next one； right？ Wrong。 I could just as easily have said there is no need for
Visual Basic properties； nor any other Visual Basic construct that enriches your programming
abilities。 The reasons we have Visual Basic properties and generics are programming
elegance and expressiveness。
To understand what I am trying to get at； consider this sentence：
Ducks walk flat feet quack loud
Reading the sentence； you get an idea of what is being said； but you are not pletely
sure。 Visual Basic without generics is like this sentence； in that you express your ideas in
code； but some things are not as clear as you would like。
Visual Basic with generics is like this sentence：
Ducks walk in a funny manner due to their flat feet； and when they quack； it is very
loud。
The sentence is clearer and uses more words to describe the same thing。 The reason we
talk using a more sophisticated language is that we want to explain concepts and be under
stood。 If you accept that； then you can accept why there is a need and context for generics。
And if not； feel free to skip this chapter and read the next one。
An example that illustrates how using generics makes your code clearer； as well as
more concise； than code that does not use generics is a container。 A container is a type
that is used to manage other types； lists and collections are examples of containers。 To keep
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286 CH AP T E R 1 1 ■ L E A R N I N G A B OU T 。 N E T G E N E R I CS
things simple； let’s look at a container that manages a single reference。 The following is the less
concise version that uses the Object type。
Public Class Container
Private _managed As Object
Public Sub New（ByVal toManage As Object）
_managed = toManage
End Sub
Public ReadOnly Property Managed（） As Object
Get
Return _managed
End Get
End Property
End Class
In the code； the class Container has a constructor with a parameter and a single property；
Managed； which references the variable _managed。 The idea beh