Smalltalk Best Practice Patterns Volume 1: Coding - Free

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SortedCollectionYou have a Collection that needs to be ordered according to some attributes of the elements.How do you sort a collection?When I was in college, sorting was a big deal. I studied Knuth. I learned a dozen clever ways tosort. I listened to all the stories about how much computing time went into sorting algorithms, andwhat an amazing impact even small improvements could have.Imagine my distress when after eleven years of Smalltalk programming I have yet to write a sortingalgorithm. All those brain cells wasted!Not wasted, of course. To be an accomplished programmer you have to know what’s going onunder the hood. It’s just that Smalltalk’s collection classes turn awareness of how sorting isimplemented into a rare and spectacular event.Just as you have collections whose order is determined by when elements were added(OrderedCollection) and unordered but efficient (Set), sorting is just another attribute of a specialkind of collection, SortedCollection.Use a SortedCollection. Set its sort block if you want to sort by some criteria other than “
ArrayYou need a Collection with a fixed number of elements. You may have been using anOrderedCollection.How do you store a collection with a fixed number of elements?OrderedCollection extols the virtues of flexibility. How many elements do you need? Why decidenow? Just use an OrderedCollection and avoid any arbitrary limits.What if you know when you create it exactly how big a collection will be? You could use anOrderedCollection and add elements, but the code would have lost the information that the size ofthe collection is fixed. Your code will communicate better if you say, “Here’s a collection. Here’show big it is. That won’t ever change.”The second reason to use a fixed size collection is efficiency. The flexibility of anOrderedCollection comes at the cost of an extra message to access elements. Most implementationsalso split OrderedCollections into two objects, so there is extra space overhead as well.Usually you don’t care about the efficiency, but I did one performance tuning gig where I got a40% speed up by replacing the OrderedCollections with Arrays. Of course, the code looked likeFORTRAN, not Smalltalk, but when you’re tuning performance you’re not out to save the world,just make it go a little faster.Use an Array. Create it with “new: anInteger” so that it has space for the number of elementsyou know it needs.Ward taught me the trick of simulating variable sized arrays. It is only valid if you are accessing theArray much more than you are adding to it and removing from it. Code that reads:children := OrderedCollection newyou change into:children := Array new “or even #()”When you need to add an element, instead of adding it to the collection:children add: anObjectyou allocate a new Array with the element added and assign it to the variable:children := children copyWith: anObjectSimilarly, for removing elements:children remove: anObjectyou allocate a new Array without the element:children := children copyWithout: anObjectUse a ByteArray to store SmallIntegers in the range 0..255. Use an Interval to represent an Array ofsequential Numbers. Use a RunArray to compactly store Arrays that have long runs of repeatedelements.Coding Patterns page 97 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
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 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 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 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
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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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