Smalltalk Best Practice Patterns Volume 1: Coding - Free

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Inject:into:You need an Enumeration that keeps a running value.How do you keep a running value as you iterate over a Collection?One of the first procedural programming patterns everyone learns is keeping a running total.1. Initialize the total2. For each element of a collection, modify the total (sum, min, max, whatever)3. Use the resultThus, you see a lot of Smalltalk code that looks like this:| max |max := 0.self children do: [:each | max := max max: each value].^maxThis is so common, in fact, that there is a message that does it for you.Why doesn’t everybody use this mysterious and powerful message? Because it has a funky name.People see the name and they think, “No way can I figure out what that does. Better leave it alone.”This is no excuse for not using it, though. When what you mean is “keep a running value over thiscollection,” you should use the message, strange name and all.Use inject:into: to keep a running value. Make the first argument the initial value. Make thesecond argument a two element block. Call the block arguments “sum” and “each”. Have theblock evaluate to the next value of the running value.The code above becomes:^self childreninject: 0into: [:sum :each | sum max: each]There is a clever use of inject:into: that I just learned. Usually I use “clever” as an insult, but I justcan’t help but show this one. The problem is iterating over adjacent pairs in a collection. That is, Iwant to evaluate some code for elements one and two, then elements two and three, and so on.Here’s how you use inject:into: for this:self childreninject: nilinto:[:eachPrevious :eachNext |eachPrevious notNil ifTrue: [...].eachNext]The first time through the loop eachPrevious is nil and eachNext is the first element of thecollection. The conditional code isn’t evaluated. The whole block evaluates to the first element ofthe collection. The second time through eachPrevious is the first element of the collection andeachNext is the second element. The conditional code gets executed. This keeps going untileachPrevious is the second to last element and eachNext is the last element.Coding Patterns page 110 of 147 9/30/2006
Collection IdiomsOnce you are comfortable using the collection protocol, you can begin using collections to solvehigher level tasks. Here are a few of the common ways collections are used.Coding Patterns page 111 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
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Pluggable BlockYou need complex Plu
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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 106 and 107: DoHow do you execute code for each
Page 108 and 109: Select/RejectHow do you execute cod
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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