Smalltalk Best Practice Patterns Volume 1: Coding - Free

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Role of PatternsReadingThese patterns are used (sometimes not in precisely the form they appear here) in the constructionof the Smalltalk images sold by the vendors. Early in your Smalltalking career you will spend mostof your time reading code from the image. If you know what to expect, and you understand why thecode is the way it is, you will be able to read and understand more quickly and thoroughly.DevelopmentDuring development you will run into the same Smalltalk problems over and over. You can usethese patterns as a guide for how to solve these problems. “What should I name this instancevariable?” - flip to Role Suggesting Instance Variable Name and follow the solution. After you usea pattern a few times, you will internalize it, so you won’t have to go looking up the details eachtime. You can put the quick reference guide up so you don’t have to program with this whole bookon your lap.ReviewGroup reviews will go much more smoothly is everyone is knows and uses the patterns. You canuse the patterns to point out opportunities for improvement in code- “I see, you need a CompleteCreation Method for that class so these three methods can be simpler.”DocumentationYou can describe a system using patterns much more simply than if you use ordinary prose. A fewwords can take the place of many paragraphs, and do a better job, because so much is implied bythe patterns. If I say, “#x:y: and #r:theta: are the Complete Creation Methods for Point,” you knowexactly what I am talking about (or will when you read Complete Creation Method on page 26).Clean UpWhen I am consulting, I clean up code using the patterns as a way of both understanding what isthere better preparing for making quick changes once I understand what’s wrong and what’srequired. I generally start with the formatting patterns (page 122), then simplify methods withComposed Method 24 and Explaining Temporary Variable 81. Once I am done with this, it is easyto see where there is duplicated code, the sign of an opportunity for improvement.Coding Patterns page 20 of 147 9/30/2006
FormatEach pattern records an atomic decision made repeatedly by experienced Smalltalk developers.They are written so you can follow them almost blindly, as just “good advice”. As yourunderstanding matures, each pattern gives you enough information that you can begin to delve intothe “why” of the pattern. After you have used a pattern enough, you should begin to understand itslimitation, when you should break the rule.Each pattern has the same format, so you can quickly scan them when you are looking for asolution to a particular problem. The following elements appear in every pattern:ElementTitlePreceding patternsProblemForcesSolutionDiscussionFollowing patternsPurposeNames the thing created as a result of executing the pattern.Intended to be used conversationally to refer to the pattern- “Oh, Ithink you need a State Object here.”Briefly describes which pattern precede this one and why. Somepatterns are nonsense taken out of order. Other orderings are theresult of experience about which problems are most important andwhich can be safely deferred.Stated as a question. Reading the problem will quickly tell youwhether you are interested in the rest of the pattern. Appears inbold face.Describes the constraints on any solution to the problem, and arguesfor the solution called for in this pattern. After reading the forcessection you should either be convinced that the solution is valid foryour situation, or you should know why the solution isn’t valid.Sometimes takes the form of a description of alternatives and whythey don’t work, sometimes just a discussion of the influences onthe design decision.Gives you an unambiguous, concrete recipe for creating the thingnamed by the title of the pattern. These will typically bedevelopment environment actions- subclass this, name this variablethus-and-so, etc. Appears in bold face.Tells you how to make practical use of the pattern. May contain anexample of use, or give you issues to watch out for.Tells you what patterns should be considered next.You can learn a lot about the patterns by just reading the titles, problems, and solutions. Indeed,that is what the pocket guide contains. When you want to go beyond the simple recipes, though,you will need to study the forces section and the links between patterns to understand their intent.Coding Patterns page 21 of 147 9/30/2006
Page 1 and 2: Smalltalk Best Practice PatternsVol
Page 3 and 4: STATE..............................
Page 5 and 6: PrefaceThis preface will explain wh
Page 7: AcknowledgmentsI would like to than
Page 10 and 11: Many of the patterns tell you what
Page 12 and 13: 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 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 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
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Role Suggesting Instance Variable N
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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
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CollectionHow do you represent a on
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RunArrayYou are using an OrderedCol
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| s |s := Set new.Like an OrderedCo
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You may need Double Dispatch for co
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DictionaryYou need a Collection tha
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SortedCollectionYou have a Collecti
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ByteArrayYou need to represent an A
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(1 to: anArray size) collect:[:each
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IsEmptyHow do you test if a collect
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ConcatentationHow do you put two co
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DoHow do you execute code for each
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Select/RejectHow do you execute cod
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Inject:into:You need an Enumeration
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Duplicate Removing SetYou have a Co
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StackHow do you implement a stack?O
Page 116 and 117:
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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