Smalltalk Best Practice Patterns Volume 1: Coding - Free

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DoHow do you execute code for each element in a collection?This is the fundamental piece out of which the rest of the enumeration messages a built. If this werea procedural language, you would have a small set of idioms for iterating through a collection, onefor a linked list, one for an array, one for a hash table.For purposes of enumeration, there is no difference between the collection classes in Smalltalk. Asa programmer you never explicitly deal with walking pointers along a list or iterating a loopcounter. You just send the message “do:” and magic happens.In spite of the simplicity of do:, I still occasionally see code where someone slips into previoushabits and writes:index := 1.[index
CollectHow do you operate not on the objects in a collection, but the result of a message sent to eachobject in the collection?If this was good old procedural programming, we’d probably write code where the enumerationblock sent a message to the element, then used the result of the message in further computation.self children do: [:each | self passJudgement: each hairStyle]Other code that also wanted to deal with hair styles would have similar code:self children do: [:each | self trim: each hairStyle]This violates the once and only once rule. The two code fragments look very similar except for theoperation to be performed on the hair style.We can capture the commonality of the code by creating an intermediate collection that containsthe results of the messages sent to each element of the original collection. We can then enumerateover the new collection.The new clarity of the code comes at the cost of allocating a new collection to hold the transformedelements and iterating over the collection twice, once to transform it and once to compute with it. Ifyou measure a performance problem with coming from intermediate collections, it is easily fixedlater. Better communication is definitely worth the cost, and chances are you’ll never have aperformance problem because of it.Use collect: to create a new collection whose elements are the results of evaluating the blockpassed to collect: with each element of the original collection. Use the new collection.We can use Composed Method with collect: to capture the common part of the above code:childrenHairStyles^self children collect: [:each | each hairStyle]Then we can simplify the code fragments:self childrenHairStyles do: [:each | self passJudgement: each]self childrenHairStyles do: [:each | self trim: each]If you must, improve performance of code using collect: with a special Enumeration Method. Use aSimple Enumeration Parameter in the block argument.Coding Patterns page 107 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
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Complete Creation MethodA Composed
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ConversionHow do you convert inform
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Converter Creation MethodYou need t
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Query MethodA Composed Method has h
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Execute Around MethodHow do you rep
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MessagesMessages are the heartbeat
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Choosing MessageYou are using a Mes
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Decomposing MessageYou are using a
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Intention Revealing SelectorYou may
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Integer>>addFloat: aFloat^self asFl
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Class: SuperFindingClientsuperclass
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Extending SuperYou are using Super.
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DelegationA Composed Method needs w
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Self DelegationYou are using Delega
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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 76 and 77: Role Suggesting Instance Variable N
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 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
Page 126 and 127: FormattingNo other topic generates
Page 128 and 129: Type Suggesting Parameter NameYou a
Page 130 and 131: Rectangular BlockYou are writing an
Page 132 and 133: Conditional ExpressionHow do you fo
Page 134 and 135: Simple Enumeration ParameterWhat sh
Page 136 and 137: self listPane parentcolor: Color bl
Page 138 and 139: Point>>printOn: aStreamaStreamprint
Page 140 and 141: Development ExampleIn this chapter,
Page 142 and 143: Money>>setAmount: aNumber currency:
Page 144 and 145: MoneySum>>printOn: aStreammonies do
Page 146: | m1 m2 |m1 := Moneyamount: 5curren
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Smalltalk Best Practice Patterns Volume 1: Coding - Free

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