Smalltalk Best Practice Patterns Volume 1: Coding - Free

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FormattingNo other topic generates more heat and less light than code formatting. Everybody has their ownstyle, and attempts to impose another style are met with ferocious resistance. So, why am I willingsticking my head into this buzz saw?The first reason is “because it is there.” I wanted to push patterns to their limit, to see how wellthey apply to a detail-oriented, exception-ridden, and emotion-filled topic. I wrote these patternsover the course of a couple of months. As new special cases came up, I either had to modify thepatterns, add a new pattern, or format my code according to the existing patterns. Before long, I nolonger was finding cases where I had to change the patterns. I am quite pleased that all offormatting in Smalltalk fits into ten patterns.The second reason is “because it is important.” Not necessarily formatting code according to thesepatterns, but formatting them according to some set of consistent rules gives a team a smoothnessto their interaction. If everybody formats the same way, then reviews and code transfer are neverdelayed while someone “cleans up” the code. Done right, formatting can convey a lot ofinformation about the structure of code at a glance.The third reason is to advance the discussion of formatting. Stating the rules as patterns makes mygoals and tradeoffs explicit. If you have a different style, you can use these patterns as an exampleto cast your own rules as patterns. Then you can compare, explicitly, what problems each set ofpatterns solves and what problems each ignores.The priorities of these patterns are:1. To make the gross structure of the method apparent at a glance. Complex messages and blocks,in particular, should jump out at the reader.2. To preserve vertical space. There is a huge difference between reading a method that fits intothe text pane of a browser and reading one that forces you to scroll. Keeping methods compactvertically lets you have smaller browsers and still be able to read methods without scrolling.This reduces window management overhead and leaves more screen space for otherprogramming tools.There are many styles of Smalltalk coding for which these formatting patterns would be a disaster.Long methods and methods that use complex expressions look terrible formatted this way.However, thorough use of Composed Method and Explaining Temporary Variable, along with theattitude that you are writing for a reader and not the computer, will go a long way towards helpingyou produce code that is simple to format and simple to read.Coding Patterns page 126 of 147 9/30/2006
Inline Message PatternYou are about to write a method for an Intention Revealing Selector.How do you format the message pattern?One alternative is to write the keyword/argument pairs one per line. This makes it easy to see whatthe selector of the method is by reading straight down from the top left corner. However, this styleof formatting will often take up three or four lines of vertical space. Composed Methods aregenerally only a few lines long. It seems a waste of space to have more introduction than content.Another reason for lining up the keywords vertically is that early text editors did not have linewrapping, so if you wanted to see all the parameters you had to scroll horizontally. All currentSmalltalks have line wrapping available in the source code editor, so all arguments are availableregardless of window size or message pattern width.The problem of reading the selector as a whole is solved by the browser. You never look at amethod as a raw piece of text. Methods always appear in the context of a browser. The selector isalways presented near the method. If you forget what method you are working on a quick glanceabove the method will answer your question.By saving the vertical space otherwise taken up by the message pattern you can quickly scan manymethods in a smaller browser than is otherwise possible. This allows you to have more informationon the screen at the same time, if it is useful.Write the message pattern without explicit line breaks.I format message patterns like this:from: fromInteger to: toInteger with: aCollection startingAt: startIntegerI’ve seen this formatted like this:from: fromIntegerto: toIntegerwith: aCollectionstartingAt: startIntegeror worse:from: fromIntegerto: toIntegerwith: aCollectionstartingAt: startIntegerBoth of these spend vertical space, increasing the chance that you won’t be able to see the body ofthe method (the part that matters, and the part that is likely to be surprising) without scrolling.Use Type Suggesting Parameter Names for parameters.Coding Patterns page 127 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
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
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 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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