Smalltalk Best Practice Patterns Volume 1: Coding - Free

More documents

Recommendations

Info

MessagesMessages are the heartbeat of a Smalltalk program. Without messages, there would be no program.Deftly managing this heartbeat is the first skill of the expert Smalltalk programmer. When youlearn to see your program in terms of patterns of messages and you learn what can be done to thatstream of messages to solve problems, then you will be able to solve any problem you can imaginein Smalltalk.Procedural languages make choices explicitly. When you code up a case statement, you say onceand for all what all the possibilities are. In Smalltalk, you use messages to make choices for you.The extra added bonus is that the set of choices is not set in concrete. You can come along later andadd new choices without affecting the existing choices just by defining a new class.This section talks about the tactical ways you can use the message stream. It gives you a toolbox oftechniques for solving problems by manipulating the communication between objects.Coding Patterns page 36 of 147 9/30/2006
MessageA Composed Method needs work done.How do you invoke computation?In the earliest days of computing, this wasn’t even a question. A program was one big routine thatexecuted from start to finish.As soon as programs got at all complicated, “program-as-a-routine” broke down. Conceptually, itwas just too hard to manipulate the whole program at once. The limited resources of the era alsocame into play. When you had the same code duplicated in many places, you could save space byusing a single copy of the code and invoking it everywhere you needed. The two factors, mentaloverload and memory overload, worked with each other. By giving the broken out parts of theroutine names, you saved space and you got a convenient tool for understanding the program apiece at a time.Here things stood for a number of years. The client would invoke a subroutine. The subroutinewould run. The client would regain control.At the same time, there was a growing realization that a disciplined use of control structures wascritical to the quality and cost of a program. If-then-else and case statements were invented tocapture common ways to vary the execution of a program.Simula brilliantly combined these two ideas. Conditional code says “execute this part of the routineor that part”. A subroutine calls says “execute that code over there”. A message says “execute thisroutine over here or that routine over there, I don’t really care.”Smalltalk went a step further by making messages the sole control structure in the system. Allprocedural control structures, conditionals and loops, are implemented in terms of messages. Forthe most part, explicit conditional logic plays a much smaller role in a Smalltalk program than aprocedural program. Messages do most of the work.Rather than invoke a routine directly, invoke a name and let the receiving object decide whatto do with it.Use Delegation to get another object to do work for you. A Choosing Message invokes one ofseveral alternatives. A Decomposing Message documents intent and provides for later refinement.An Intention Revealing Message maps intention to implementation. User Super to invoke behaviorin a superclass.Coding Patterns page 37 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 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 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
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 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
Page 146:
| m1 m2 |m1 := Moneyamount: 5curren
show all

Smalltalk Best Practice Patterns Volume 1: Coding - Free

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?