Smalltalk Best Practice Patterns Volume 1: Coding - Free

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Role Suggesting Instance Variable NameYou need to name Common State.What should you name an instance variable?The two important pieces of information to communicate about any variable are:What is its purpose?How is it used?The purpose or role of a variable is important to the reader because it helps direct their attentionappropriately. Typically when you read code you have a purpose in mind. If you understand therole of a variable and it is unrelated to your purpose, you can quickly skim over irrelevant code thatuses that variable. Likewise, if you see a variable that is related to your purpose you can quicklynarrow your reading to relevant code by looking for that variable.How a variable is used, the messages it is sent, are its “type”. Smalltalk doesn’t have declaredtypes, but that doesn’t mean they aren’t important. Understanding the messages sent to a variabletells you what objects can be safely placed as values in that variable. Substitution of objects is theheart of disciplined maintenance and reuse.Different variables appear in different contexts, so what you need to communicate with their namesis different. The context for instance variables is most similar to the context for temporaryvariables. The only way you have for communicating the role of an instance variable is through itsname. If the variables in Point were called “t1” and “t2” instead of “x” and “y”, you’d have a lot ofreading to do before you could tell which was the horizontal component and which the vertical.Naming the variables by their roles gives you that information directly.On the other hand, the type of an instance variable is easily discovered from the code in which itresides. It is easy to find where the variable is used, and from there discover what messages it issent. You also get hints from Creation Parameter Setting Methods or Setting Methods that set thevalue of the variable. If I asked you what the type of “x” was in:Point>>x: aNumberx := aNumberyou’d be able to tell me instantly. In the interest of keeping names simple, short, and readable, youcan safely leave out any mention of the type of a variable in its name.Name instance variables for the role they play in the computation. Make the name plural ifthe variable will hold a Collection.Coding Patterns page 76 of 147 9/30/2006
Temporary VariablesTemporary variables let you store and reuse the value of expressions. They can be used to improvethe performance or readability of methods. The following patterns motivate and guide the use oftemporary variables. The examples are taken from Smalltalk, but the discussion applies to anylanguage with procedure-scoped variables.Coding Patterns page 77 of 147 9/30/2006
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Smalltalk Best Practice PatternsVol
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STATE..............................
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PrefaceThis preface will explain wh
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AcknowledgmentsI would like to than
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Many of the patterns tell you what
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day to day in development and docum
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What’s Missing?There are a few co
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AdoptionHow can you learn and use t
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Why Patterns WorkHere is the Big As
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Role of PatternsReadingThese patter
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BehaviorObjects model the world thr
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Composed MethodYou are implementing
Page 26 and 27: Complete Creation MethodA Composed
Page 28 and 29: ConversionHow do you convert inform
Page 30 and 31: Converter Creation MethodYou need t
Page 32 and 33: Query MethodA Composed Method has h
Page 34 and 35: Execute Around MethodHow do you rep
Page 36 and 37: MessagesMessages are the heartbeat
Page 38 and 39: Choosing MessageYou are using a Mes
Page 40 and 41: Decomposing MessageYou are using a
Page 42 and 43: Intention Revealing SelectorYou may
Page 44 and 45: Integer>>addFloat: aFloat^self asFl
Page 46 and 47: Class: SuperFindingClientsuperclass
Page 48 and 49: Extending SuperYou are using Super.
Page 50 and 51: DelegationA Composed Method needs w
Page 52 and 53: Self DelegationYou are using Delega
Page 54 and 55: Pluggable BehaviorHow can you param
Page 56 and 57: Pluggable BlockYou need complex Plu
Page 58 and 59: marriedMenAndUnmarriedWomen^self ma
Page 60 and 61: Instance VariablesI wrote the secti
Page 62 and 63: Variable StateHow do you represent
Page 64 and 65: Timer>>defaultMillisecondPeriod^100
Page 66 and 67: Default Value MethodYou have a comp
Page 68 and 69: Direct Variable AccessYou need to a
Page 70 and 71: Getting MethodYou are using Lazy In
Page 72 and 73: Collection Accessor MethodYou are u
Page 74 and 75: Enumeration MethodYou are using Ind
Page 78 and 79: Temporary VariableA Composed Method
Page 80 and 81: Caching Temporary VariableA Perform
Page 82 and 83: Reusing Temporary VariableTemporary
Page 84 and 85: CollectionsThe collection hierarchy
Page 86 and 87: CollectionHow do you represent a on
Page 88 and 89: RunArrayYou are using an OrderedCol
Page 90 and 91: | s |s := Set new.Like an OrderedCo
Page 92 and 93: You may need Double Dispatch for co
Page 94 and 95: DictionaryYou need a Collection tha
Page 96 and 97: SortedCollectionYou have a Collecti
Page 98 and 99: ByteArrayYou need to represent an A
Page 100 and 101: (1 to: anArray size) collect:[:each
Page 102 and 103: IsEmptyHow do you test if a collect
Page 104 and 105: ConcatentationHow do you put two co
Page 106 and 107: DoHow do you execute code for each
Page 108 and 109: Select/RejectHow do you execute cod
Page 110 and 111: Inject:into:You need an Enumeration
Page 112 and 113: Duplicate Removing SetYou have a Co
Page 114 and 115: StackHow do you implement a stack?O
Page 116 and 117: implementation of queues in Pascal
Page 118 and 119: Lookup CacheHow do you optimize com
Page 120 and 121: Parsing StreamHow do you write a si
Page 122 and 123: ClassesThere is probably no coding
Page 124 and 125: Qualified Subclass NameYou have cre
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FormattingNo other topic generates
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Type Suggesting Parameter NameYou a
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Rectangular BlockYou are writing an
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Conditional ExpressionHow do you fo
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Simple Enumeration ParameterWhat sh
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self listPane parentcolor: Color bl
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Point>>printOn: aStreamaStreamprint
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Development ExampleIn this chapter,
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Money>>setAmount: aNumber currency:
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MoneySum>>printOn: aStreammonies do
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| m1 m2 |m1 := Moneyamount: 5curren
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Smalltalk Best Practice Patterns Volume 1: Coding - Free

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