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interfaces like System。IO。TextReader and System。IO。TextWriter。
Assigning the console streams involves assigning the properties In and Out to TextReader
and TextWriter； respectively。 The code that calls the processor。Process（） method sends a
stream to the processor and awaits a response that is sent as another stream。
Knowing that TextReader and TextWriter are general interfaces； or technically abstract
base classes； you could be tempted to redesign the IProcessor interface as follows：
Public Interface IProcessor
Function Process（ByVal input As TextReader； ByVal output As TextWriter）
End Interface
There is nothing wrong with this declaration of IProcessor； but I would not be tempted to
use it because it relies on the interfaces TextReader and TextWriter。 In the case of our example；
that is acceptable； and you might find that it is good enough for your application。 But I like to
keep things general and then be more specific when necessary。 Later in this chapter； when we
work with binary data streams； we will need to be specific and will use an interface declaration
similar to the one shown here。
■Note As a general rule of thumb； it is always easy to write specific code because you have easy access
to the methods and properties you need。 It is harder from a design perspective to keep things general。 The
advantage of keeping things general is your code is more flexible and can be used in multiple contexts。
However； you shouldn’t make it a hard rule that all code will be general。 The rule of thumb is to try to stay as
general as possible using interfaces and have the implementation define the specifics。
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256 CH AP T E R 1 0 ■ L E A R N I N G A B OU T P E R S IS TE N CE
Having implemented all of the pieces； you could pile the source code and run the
mand to read piped data。 The only thing missing is the file that contains the data；
lotto。txt。 For the example； create a file called lotto。txt and add text such as the following；
where each line represents the date of the lottery draw； then the six lottery numbers； and then
the bonus number （you could also use the lotto。txt file included with this book’s download
able code）。
1970。01。10 7 8 12 17 32 40 24
1970。01。17 7 12 22 24 29 40 36
1970。01。24 16 22 25 27 30 35 24
1970。01。31 3 11 21 22 24 39 8
1970。02。07 2 5 11 16 18 38 37
Now run the following piping mand （open a mand prompt and navigate to
TextProcessorTextProcessorbinRelease from the Visual Basic Express base directory）：
type lotto。txt ｜ TextProcessor。exe
You should see the contents of lotto。txt。 If that is what you get； you have a successful
round…trip and have created all of the puzzle pieces。
REMEMBERING TO IMPLEMENT ALL THE PIECES
Some readers may argue that having an echo implemented in LottoTicketProcessor is the wrong
approach because there might be a munication failure among team members； leading to buggy code。
Also； you might miss implementing some code； creating bugs when there should not have been any。 Although
those risks are involved； this approach has important benefits； and there are ways to mitigate the risks。
One of the challenges for Visual Basic developers is knowing not only the language； but also the API。
This book will not talk about the API because you could die of old age before you read everything there is to
know about the API。
The API is vast； but you will not need to use all of the API all the time。 What you need to be aware
of are the general classes of the API。 What part of the API is used to read and write streams？ What part of the
API is used to create GUI elements？ This means you are not ever going to be an expert on all parts of the API；
although you might be an expert Visual Basic programmer and understand the general concepts。
When I understand a domain quite well； I develop using a bottom…up approach。 This works because I
know which interface and implementation need to talk to which other interface and implementation。 When I
don’t understand a domain fully； I develop using a top…down approach。 Using a top…down approach； I can figure
out what the pieces are in a simplified manner。 I create my echo program； which gives a plete round…trip
without getting bogged down in the details of the API。
Think of a bunch of guys putting together a barbecue grill。 They might look at the instructions； but more
likely； they will look at the parts and try to mentally fit the pieces together。 They might even put a couple of
pieces together to get an idea of what each piece does and how the overall grill should appear。 Once they
bee confident of their prototype； they build the real thing； which hopefully resembles a barbecue grill。
When you use this approach； what you are doing is building a mockup； proof of concept； or prototype。
Maybe two or three team members might help develop this prototype； but the fact that your code needs to be
declared as a prototype is extremely important。
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Visual Basic Express and the Visual Studio products help you in that they allow you to embed task markers。 Go
back to the source code example where LottoTicketProcessor was illustrated and look at the ment：
' TODO： Finish implementing the class
Notice TODO is in all capital letters。 That type of ment is special。 It is called a task and is tracked by
Visual Basic Express in the Task List window。 To open ments in the Task List window； select View Other
Windows Task List； and then select ments from the drop…down list at the top of the window。
This allows a team of developers to add markers throughout the entire code base； indicating what is done
and not done。 That way； you will not forget to do certain tasks。
Some other identifiers that you can use are HACK to identify some code that is not correct； but hacked in so
that it works； and UNDONE。 If you happen to be using a Visual Studio edition other than Express； you can define
your own ment identifiers。 For more information； see the MSDN article “Visual Studio How to： Create Custom
ment Tokens” （http：//msdn2。microsoft。/en…US/library/ekwz6akh（VS。80）。aspx）。
Implementing Stream Reading and Writing
Finishing the stream reading and writing means looking at the possible arguments that can be
given； and then implementing the code to process the arguments。 Here is the plete source
code for ReaderWriter。Bootstrap：
#Const DEBUG_OUTPUT = True
Imports System。IO
Public Module Bootstrap
Public Sub DisplayHelp（）
Console。WriteLine（〃You need help？ Right now？〃）
End Sub
Public Sub Start（ByVal args As String（）； ByVal processor As IProcessor）
#If DEBUG_OUTPUT Then
Console。WriteLine（〃Argument count（〃 & args。Length & 〃）〃）
For Each argument As String In args
Console。WriteLine（〃Argument （〃 & argument & 〃）〃）
Next
#End If
Dim reader As TextReader = Nothing
Dim writer As