Smalltalk Best Practice Patterns Volume 1: Coding - Free

More documents

Recommendations

Info

MoneySum>>printOn: aStreammonies do:[:each |aStreamprint: each;nextPutAll: ' + '].aStream skip: -3We used a basketful of patterns in this method: Direct Variable Access, Role Suggesting ParameterName, Simple Enumeration Parameter, Rectangular Block, Indented Control Flow, and Do.With MoneySum in hand, we can modify Money>>+ to return a MoneySum if the two currenciesdon’t match:Money>>+ aMoney^currency = aMoney currencyifTrue:[self speciesamount: amount + aMoney amountcurrency: currency]ifFalse:[MoneySum monies: (Arraywith: selfwith: aMoney)]We need a Getting Method for Money’s currency:Money>>currency^currencyNow our multi-currency example works:| m1 m2 |m1 := Moneyamount: 5currency: #USD.m2 := Moneyamount: 7currency: #GBP.m1 + m2 5 USD + 7 GBPJust to check, the single currency example works, still:| m1 m2 |m1 := Moneyamount: 5currency: #USD.m2 := Moneyamount: 7currency: #USD.m1 + m2 12 USDCoding Patterns page 144 of 147 9/30/2006
IntegrationFor a MoneySum to truly be an Impostor for a Money, it has to support all the same messages. Allthe combinations of Moneys and MoneySums have to work together. We will use Double Dispatchto implement this. Double Dispatch states: “Send a message to the argument. Append the classname of the receiver to the selector. Pass the receiver as an argument.” Money addition becomes:Money>> + aMoneyâMoney addMoney: selfThe old Money>>+ becomes Money>>addMoney:Money>>addMoney: aMoney^currency = aMoney currencyifTrue:[self speciesamount: amount + aMoney amountcurrency: currency]ifFalse:[MoneySum monies: (Arraywith: selfwith: aMoney)]MoneySum arithmetic follows the Double Dispatch pattern, too:MoneySum>> + aMoneyâMoney addMoneySum: selfIf a MoneySum is adding a Money, it should produce a new MoneySum with the Money added tothe list of Monies:MoneySum>>addMoney: aMoney^self species monies: (monies copyWith: aMoney)Now we can send “+” to a Money with a MoneySum as argument:| m1 m2 |m1 := Moneyamount: 5currency: #USD.m2 := Moneyamount: 7currency: #GBP.m1 + (m2 + m1) 5 USD + 7 GBP + 5 USDTo complete the Double Dispatch, we have to implement addMoneySum: in Money andMoneySum. The implementation in Money is simple, we just turn around and send addMoney: tothe MoneySum, trusting the existing implementation to work:Money>> addMoneySum: aMoneySumâMoneySum addMoney: selfWe can test this:Coding Patterns page 145 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 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
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 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?