Smalltalk Best Practice Patterns Volume 1: Coding - Free

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Point>>printOn: aStreamaStreamprint: self x;nextPut: $@;print: self yHaving written this, I’m not sure why I prefer Cascades to the parenthesized format. Perhaps it’sbecause there is a big psychological difference in parsing a method with parentheses and onewithout. If I can avoid parentheses and still have a method that reads clearly, I will.Another use of yourself is with #inject:into:. Suppose you want to put all the children of acollection of parents together in a Set. You might be tempted to write:parentsinject: Set newinto: [:sum :each | sum addAll: each children]but this wouldn’t work, because the result of sending #addAll: is the argument (in this case thechildren), not the receiver. To get this to work as expected, you have to write:parentsinject: Set newinto: [:sum :each | sum addAll: each children; yourself]Coding Patterns page 138 of 147 9/30/2006
Interesting Return ValueWhen should you explicitly return a value at the end of a method?All messages sends return a value. If a method does not explicitly return a value, the receiver ofthe message is returned by default. This causes some confusion for new programmers, who may beused to Pascal's distinction between procedures and functions, or C's lack of a definition of thereturn value of a procedure with no explicit return. To compensate, some programmers alwaysexplicitly return a value from every method.The distinction between methods that do their work by side effect and those that are valuable forthe result they return is important. An unfamiliar reader wanting to quickly understand theexpected use of a method should be able to glance at the last line and instantly understand whethera useful return value is generated or not. Therefore:Return a value only when you intend for the sender to use the value.For example, consider the implementation of topComponent in VisualWorks. Visual componentsform a tree, with a ScheduledWindow at the root. Any component in the tree can fetch the root, bysending itself the message "topComponent". VisualPart (the superclass of interior nodes andleaves) implements this message by asking the container for its topComponent:VisualPart>>topComponent^container topComponentScheduledWindow implements the base case of the recursion by returning itself. The simplestimplementation would be to have a method with no statements. It would return the receiver.However, using Interesting Return Value, because the result is intended to be used by the sender, itexplicitly returns "self".ScheduledWindow>>topComponent^selfCoding Patterns page 139 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
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Instance VariablesI wrote the secti
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Variable StateHow do you represent
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Timer>>defaultMillisecondPeriod^100
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Default Value MethodYou have a comp
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Direct Variable AccessYou need to a
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Getting MethodYou are using Lazy In
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Collection Accessor MethodYou are u
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Enumeration MethodYou are using Ind
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Role Suggesting Instance Variable N
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Temporary VariableA Composed Method
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Caching Temporary VariableA Perform
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Reusing Temporary VariableTemporary
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CollectionsThe collection hierarchy
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CollectionHow do you represent a on
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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
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 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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