Smalltalk Best Practice Patterns Volume 1: Coding - Free

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Timer>>defaultMillisecondPeriod^1000Timer>>initializecount := 0.period := self defaultMillisecondPeriodUse Default Value Method to explain any value that isn’t obvious. Initialize Methods in a hierarchycommonly need Extending Super to finish their job.Coding Patterns page 64 of 147 9/30/2006
Lazy InitializationYou are initializing Common State.How do you initialize an instance variable to its default value?Here is the flip side of variable initialization. All the strengths of Explicit Initialization becomeweaknesses and all the weaknesses strengths.Lazy Initialization breaks initialization into two methods per variable. The first is a Getting Methodthat hides the fact that the variable is lazily initialized from anyone wanting to use its value. Thisimplies that there can be no Direct Variable Access. The second method, the Default ValueMethod, provides the default value of the variable.This is where the flexibility comes in. If you make a subclass, you can change the default value byoverriding the Default Value Method.Readability suffers because there isn’t any one place you can look to see all the variables and theirinitial values. Instead, you have to look at several methods to see all the values.Performance is another reason to use a Lazy Initialization. Expensive initialization that may not beneeded for a while (or at all) can be deferred by using Lazy Initialization.Writing a Getting Method for the variable. Initialize it if necessary with a Default ValueMethod.The Timer example from above needs no explicit initialization. Instead, count is initialized in itsGetting Method:Timer>>countcount isNil ifTrue: [count := defaultCount].^countAnd the default value comes from its own method:Timer>>defaultCount^0Similarly for period:Timer>>periodperiod isNil ifTrue: [period := self defaultPeriod].^periodTimer>>defaultPeriod^1000Some people swear by Lazy Initialization. They go so far as to say that all initialization should bedone this way. I actually lean towards Explicit Initialization. Too many times I’ve bent overbackwards to supply lots of flexibility that is never used. I’d rather do it the simple way first, thenfix it if it’s a problem. However, if I know I am writing code that is likely to be subclassed byothers, I’ll go ahead and Lazy Initialization from the first.A Default Value Method supplies a default value. A Compute Method supplies the value of anCaching Instance Variable.Coding Patterns page 65 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
Page 14 and 15: What’s Missing?There are a few co
Page 16 and 17: AdoptionHow can you learn and use t
Page 18 and 19: Why Patterns WorkHere is the Big As
Page 20 and 21: Role of PatternsReadingThese patter
Page 22 and 23: BehaviorObjects model the world thr
Page 24 and 25: 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 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 110 and 111: Inject:into:You need an Enumeration
Page 112 and 113: Duplicate Removing SetYou have a Co
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StackHow do you implement a stack?O
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implementation of queues in Pascal
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Lookup CacheHow do you optimize com
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Parsing StreamHow do you write a si
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ClassesThere is probably no coding
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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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