8 - oop - smalltalk syntax

Stéphane Ducasse 1

Stéphane Ducassestephane.ducasse@inria.frhttp://stephane.ducasse.free.fr/

A Little Journey in the Smalltalk Syntax

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Goal

Lower your stress :)Show you that this is simple

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Appetizer!

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Yeah!

Smalltalk is a dynamically typed language

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ArrayList<String> strings = new ArrayList<String>();

strings := ArrayList new.

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ShorterThread regThread = new Thread( new Runnable() { public void run() { this.doSomething();} }); regThread.start();

[self doSomething] fork.

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Smalltalk = Objects + Messages + (...)

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RoadmapFun with numbers

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1 class

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1 class >SmallInteger

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1 class maxVal

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1 class maxVal>1073741823

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1 class maxVal + 1

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1 class maxVal + 1>1073741824

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(1 class maxVal + 1) class

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(1 class maxVal + 1) class>LargePositiveInteger

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(1/3) + (2/3)

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(1/3) + (2/3)>1

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2/3 + 1

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2/3 + 1> 5/3

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1000 factorial

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1000 factorial 402387260077093773543702433923003985719374864210714632543799910429938512398629020592044208486969404800479988610197196058631666872994808558901323829669944590997424504087073759918823627727188732519779505950995276120874975462497043601418278094646496291056393887437886487337119181045825783647849977012476632889835955735432513185323958463075557409114262417474349347553428646576611667797396668820291207379143853719588249808126867838374559731746136085379534524221586593201928090878297308431392844403281231558611036976801357304216168747609675871348312025478589320767169132448426236131412508780208000261683151027341827977704784635868170164365024153691398281264810213092761244896359928705114964975419909342221566832572080821333186116811553615836546984046708975602900950537616475847728421889679646244945160765353408198901385442487984959953319101723355556602139450399736280750137837615307127761926849034352625200015888535147331611702103968175921510907788019393178114194545257223865541461062892187960223838971476088506276862967146674697562911234082439208160153780889893964518263243671616762179168909779911903754031274622289988005195444414282012187361745992642956581746628302955570299024324153181617210465832036786906117260158783520751516284225540265170483304226143974286933061690897968482590125458327168226458066526769958652682272807075781391858178889652208164348344825993266043367660176999612831860788386150279465955131156552036093988180612138558600301435694527224206344631797460594682573103790084024432438465657245014402821885252470935190620929023136493273497565513958720559654228749774011413346962715422845862377387538230483865688976461927383814900140767310446640259899490222221765904339901886018566526485061799702356193897017860040811889729918311021171229845901641921068884387121855646124960798722908519296819372388642614839657382291123125024186649353143970137428531926649875337218940694281434118520158014123344828015051399694290153483077644569099073152433278288269864602789864321139083506217095002597389863554277196742822248757586765752344220207573630569498825087968928162753848863396909959826280956121450994871701244516461260379029309120889086942028510640182154399457156805941872748998094254742173582401063677404595741785160829230135358081840096996372524230560855903700624271243416909004153690105933983835777939410970027753472000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000

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1000 factorial / 999 factorial

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1000 factorial / 999 factorial> 1000

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10 @ 100

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10 @ 100

(10 @ 100) x

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10 @ 100

(10 @ 100) x> 10

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10 @ 100

(10 @ 100) x> 10

(10 @ 100) y

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10 @ 100

(10 @ 100) x> 10

(10 @ 100) y>100

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Points!

Points are created using @

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Puzzle

(10@100) + (20@100)

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Puzzle

(10@100) + (20@100) >30@200

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Puzzle

(10@100) + (20@100) >30@200

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RoadmapFun with characters, strings, arrays

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$C $h $a $r $a $c $t $e $r

$F, $Q $U $E $N $T $i $N

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space tab?!

Character spaceCharacter tabCharacter cr

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‘Strings’

‘Tiramisu’

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Characters

12 printString

> ’12’

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Strings are collections of chars

‘Tiramisu’ at: 1

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Strings are collections of chars

‘Tiramisu’ at: 1

> $T

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A program! -- finding the last char

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A program!

| str |

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A program!

| str | local variable

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A program!

| str | local variablestr := ‘Tiramisu’.

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A program!

| str | local variablestr := ‘Tiramisu’. assignment

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A program!

| str | local variablestr := ‘Tiramisu’. assignmentstr at: str length

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A program!

| str | local variablestr := ‘Tiramisu’. assignmentstr at: str length message send

> $u

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double ‘ to get one

‘L’’Idiot’

> one string

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For concatenation use ,

‘Calvin’ , ‘ & ‘, ‘Hobbes’

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For concatenation use ,

‘Calvin’ , ‘ & ‘, ‘Hobbes’> ‘Calvin & Hobbes’

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For concatenation use ,

‘Calvin’ , ‘ & ‘, ‘Hobbes’> ‘Calvin & Hobbes’

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Symbols: #Pharo

#Something is a symbol

Symbol is a unique string in the system

#Something == #Something > true

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“Comment”

“what a fun language lecture.I really liked the desserts”

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#(Array)

#(‘Calvin’ ‘hates’ ‘Suzie’)

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#(Array)

#(‘Calvin’ ‘hates’ ‘Suzie’) size

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#(Array)

#(‘Calvin’ ‘hates’ ‘Suzie’) size> 3

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First element starts at 1

#(‘Calvin’ ‘hates’ ‘Suzie’) at: 2

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First element starts at 1

#(‘Calvin’ ‘hates’ ‘Suzie’) at: 2> ‘hates’

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at: to access, at:put: to set

#(‘Calvin’ ‘hates’ ‘Suzie’) at: 2 put: ‘loves’

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#(Array)

#(‘Calvin’ ‘hates’ ‘Suzie’) at: 2 put: ‘loves’

> #(‘Calvin’ ‘loves’ ‘Suzie’)

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Syntax Summarycomment: “a comment”character: $c $h $a $r $a $c $t $e $r $s $# $@ string: ‘a nice string’ ‘lulu’ ‘l’’idiot’symbol: #mac #+ array: #(1 2 3 (1 3) $a 4)byte array: #[1 2 3]integer: 1, 2r101real: 1.5, 6.03e-34,4, 2.4e7fraction: 1/33boolean: true, falsepoint: 10@120

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RoadmapFun with keywords-based messages

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Keyword-based messages

arr at: 2 put: ‘loves’

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Keyword-based messages

arr at: 2 put: ‘loves’

somehow like arr.atput(2,‘loves’)

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From Java to Smalltalk

postman.send(mail,recipient);

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Removing

postman.send(mail,recipient);

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Removing unnecessary

postman send mail recipient

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But without losing information

postman send mail to recipient

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postman send: mail to: recipient

postman.send(mail,recipient);

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postman send: mail to: recipient

The message is send:to:

postman.send(mail,recipient);

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RoadmapFun with variables

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Shared or Global starts with Uppercase

Transcript cr .Transcript show: ‘hello world’.Transcript cr .

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local or temps starts with lowercase

| str |str := ‘Tiramisu’

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self, super, true, false, nil

self = thissuper

true, false are for Booleans

nil is UndefinedObject instance

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self, super, true, false, nil

self = this in Javasuper

true, false are for Booleans

nil is UndefinedObject instance

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RoadmapFun with classes

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A class definition!

Superclass subclass: #ClassinstanceVariableNames: 'a b c'

...category: 'Package name'

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A class definition!

Object subclass: #PointinstanceVariableNames: 'x y'classVariableNames: ''poolDictionaries: ''category: 'Graphics-Primitives'

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A class definition!

Object subclass: #PointinstanceVariableNames: 'x y'classVariableNames: ''poolDictionaries: ''category: 'Graphics-Primitives'

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RoadmapFun with methods

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On Integer

asComplex"Answer a Complex number that represents value of the the receiver."

^ Complex real: self imaginary: 0

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On Boolean

xor: aBoolean "Exclusive OR. Answer true if the receiver is not equivalent to aBoolean."

^(self == aBoolean) not

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Summary

self, supercan access instance variablescan define local variable | ... |Do not need to define argument types^ to return

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RoadmapFun with unary messages

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1 class

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1 class> SmallInteger

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false not

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false not> true

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Date today

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Date today> 24 May 2009

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Time now

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Time now> 6:50:13 pm

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Float pi

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Float pi> 3.141592653589793

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We sent messages to objects or classes!

1 classDate today

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We sent messages to objects or classes!

1 classDate today

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Fun with binary messages

Roadmap

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aReceiver aSelector anArgument

Used for arithmetic, comparison and logical operationsOne or two characters taken from: + - / \ * ~ < > = @ % | & ! ? ,

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1 + 2

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1 + 2>3

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2 => 3

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2 => 3> false

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10 @ 200

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‘Black chocolate’ , ‘ is good’

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RoadmapFun with keyword-based messages

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#(‘Calvin’ ‘hates’ ‘Suzie’) at: 2 put: ‘loves’

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#(‘Calvin’ ‘hates’ ‘Suzie’) at: 2 put: ‘loves’> #(‘Calvin’ ‘loves’ ‘Suzie’)

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10@20 setX: 2

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10@20 setX: 2> 2@20

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12 between: 10 and: 20

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12 between: 10 and: 20> true

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receiver keyword1: argument1

keyword2: argument2

equivalent to receiver.keyword1keyword2(argument1, argument2)

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receiver keyword1: argument1

keyword2: argument2

equivalent to receiver.keyword1keyword2(argument1, argument2)

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Browser newOnClass: Point

Roadmap

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Browser newOnClass: Point

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Browser newOnClass: Point

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Yes there is a difference between doing (side effect)and returning an object

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Browser newOnClass: Point> a Browser

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Doing and do not care of the returned result

Browser newOnClass: Point

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Doing and really want to see the result!

10@20 setX: 2> 2@20

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Doing vs printing (doing + print result)

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Doing vs printing (doing + print result)

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RoadmapMessages messagesmessagesagain messages....

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Yes there are only messages unary binary keywords

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Composition: from left to right!

69 class inspect

69 class superclass superclass inspect

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Unary> Binary> Keywords

Precedence

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2 + 3 squared

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2 + 3 squared> 2 + 9

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2 + 3 squared> 2 + 9> 11

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Color gray - Color white = Color black

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Color gray - Color white = Color black> aColor = Color black

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Color gray - Color white = Color black> aColor = Color black> true

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2 raisedTo: 3 + 2

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2 raisedTo: 3 + 2> 2 raisedTo: 5

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2 raisedTo: 3 + 2> 2 raisedTo: 5> 32

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1/3 + 2/3

No mathematical precedence

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1/3 + 2/3>7/3 /3

No mathematical precedence

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Parenthesized takes precedence!

(Msg) > Unary> Binary> Keywords

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(0@0 extent: 100@100) bottomRight

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(0@0 extent: 100@100) bottomRight> (aPoint extent: anotherPoint) bottomRight

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(0@0 extent: 100@100) bottomRight> (aPoint extent: anotherPoint) bottomRight> aRectangle bottomRight

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(0@0 extent: 100@100) bottomRight> (aPoint extent: anotherPoint) bottomRight> aRectangle bottomRight> 100@100

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0@0 extent: 100@100 bottomRight

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0@0 extent: 100@100 bottomRight> Message not understood> 100 does not understand bottomRight

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3 + 2 * 10

No mathematical precedence

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3 + 2 * 10> 5 * 10

No mathematical precedence

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3 + 2 * 10> 5 * 10> 50 argh!

No mathematical precedence

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3 + (2 * 10)

No mathematical precedence

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3 + (2 * 10)> 3 + 20

No mathematical precedence

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3 + (2 * 10)> 3 + 20> 23

No mathematical precedence

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1/3 + 2/3> 7/3 /3

No mathematical precedence

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1/3 + 2/3> (7/3) /3> 7/9

No mathematical precedence

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(1/3) + (2/3)

No mathematical precedence

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(1/3) + (2/3)> 1

No mathematical precedence

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(Msg) > Unary > Binary > Keywordsfrom left to rightNo mathematical precedence

Only Messages

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(Msg) > Unary > Binary > Keywordsfrom left to rightNo mathematical precedence

Only Messages

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RoadmapFun with blocks

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Function definition

fct(x) = x * x + x

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Function Application

fct (2) = 6fct (20) = 420

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Function definition

fct(x) = x * x + x

|fct|fct:= [:x | x * x + x].

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Function Application

fct (2) = 6fct (20) = 420

fct value: 2 > 6fct value: 20 > 420

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Other examples

[2 + 3 + 4 + 5] value[:x | x + 3 + 4 + 5 ] value: 2[:x :y | x + y + 4 + 5] value: 2 value: 3

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Block

anonymous method

[ :variable1 :variable2 | | tmp |expression1....variable1 ... ]

value: ...

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Block

anonymous methodReally really cool!Can be passed to methods, stored in instance variables

[ :variable1 :variable2 | | tmp |expression1....variable1 ... ]

value: ...

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RoadmapFun with conditional

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Example

3 > 0 ifTrue:['positive'] ifFalse:['negative']

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Example

3 > 0 ifTrue:['positive'] ifFalse:['negative']

> ‘positive’

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Yes ifTrue:ifFalse: is a message!

Weather isRaining ifTrue: [self takeMyUmbrella] ifFalse: [self takeMySunglasses]

ifTrue:ifFalse is sent to an object: a boolean!

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Booleans

& | notor: and: (lazy)xor:ifTrue:ifFalse:ifFalse:ifTrue:...

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Yes! ifTrue:ifFalse: is a message send to a Boolean.

But optimized by the compiler :)

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10 timesRepeat: [ Transcript show: 'hello'; cr]

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10 timesRepeat: [ Transcript show: 'hello'; cr]

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[x<y] whileTrue: [x := x + 3]

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aBlockTest whileTrueaBlockTest whileFalseaBlockTest whileTrue: aBlockBodyaBlockTest whileFalse: aBlockBodyanInteger timesRepeat: aBlockBody

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Confused with () and [] ?

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Only put [ ] when you do not the number of times something may be executed

(x isBlue) ifTrue: [ x schroumph ]

10 timesRepeat: [ self shout ]

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Conditions are messages sent to boolean

(x isBlue) ifTrue: [ ]

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Fun with loops

Roadmap

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1 to: 100 do: [ :i | Transcript show: i ; space]

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1 to: 100 do: [ :i | Transcript show: i ; space]

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1 to: 100 by: 3 do: [ :i | Transcript show: i ; space]

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1 to: 100 by: 3 do: [ :i | Transcript show: i ; space]

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So yes there are real loops in Smalltalk!

to:do: to:by:do:are just messages send to integers

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So yes there are real loops in Smalltalk!

to:do: to:by:do:are just messages send to integers

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RoadmapFun with iterators

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ArrayList<String> strings = new ArrayList<String>(); for(Person person: persons) strings.add(person.name());

strings := persons collect [:person | person name].

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#(2 -3 4 -35 4) collect: [ :each| each abs]

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#(2 -3 4 -35 4) collect: [ :each| each abs]> #(2 3 4 35 4)

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#(15 10 19 68) collect: [:i | i odd ]

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#(15 10 19 68) collect: [:i | i odd ]> #(true false true false)

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#(15 10 19 68) collect: [:i | i odd ]

We can also do it that way!

|result|aCol := #( 2 -3 4 -35 4).result := aCol species new: aCol size.1 to: aCollection size do:

[ :each | result at: each put: (aCol at: each) odd].result

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#(15 10 19 68) do: [:i | Transcript show: i ; cr ]

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#(15 10 19 68) do: [:i | Transcript show: i ; cr ]

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#(1 2 3) with: #(10 20 30) do: [:x :y| Transcript show: (y ** x) ; cr ]

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#(1 2 3) with: #(10 20 30) do: [:x :y| Transcript show: (y ** x) ; cr ]

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How do: is implemented?

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How do: is implemented?

SequenceableCollection>>do: aBlock "Evaluate aBlock with each of the receiver's elements as the argument."

1 to: self size do: [:i | aBlock value: (self at: i)]

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Some others... friends

#(15 10 19 68) select: [:i|i odd]

#(15 10 19 68) reject: [:i|i odd]

#(12 10 19 68 21) detect: [:i|i odd]

#(12 10 12 68) detect: [:i|i odd] ifNone:[1]

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Some others... friends

#(15 10 19 68) select: [:i|i odd] > #(15 19)

#(15 10 19 68) reject: [:i|i odd]

#(12 10 19 68 21) detect: [:i|i odd]

#(12 10 12 68) detect: [:i|i odd] ifNone:[1]

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Some others... friends

#(15 10 19 68) select: [:i|i odd] > #(15 19)

#(15 10 19 68) reject: [:i|i odd] > #(10 68)

#(12 10 19 68 21) detect: [:i|i odd]

#(12 10 12 68) detect: [:i|i odd] ifNone:[1]

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Some others... friends

#(15 10 19 68) select: [:i|i odd] > #(15 19)

#(15 10 19 68) reject: [:i|i odd] > #(10 68)

#(12 10 19 68 21) detect: [:i|i odd] > 19

#(12 10 12 68) detect: [:i|i odd] ifNone:[1]

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Some others... friends

#(15 10 19 68) select: [:i|i odd] > #(15 19)

#(15 10 19 68) reject: [:i|i odd] > #(10 68)

#(12 10 19 68 21) detect: [:i|i odd] > 19

#(12 10 12 68) detect: [:i|i odd] ifNone:[1]> 1

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Iterators are your best friends compact nice abstraction Just messages sent to collections

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Iterators are your best friends compact nice abstraction Just messages sent to collections

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A simple exercise

How do you define the method that does that?

#() -> ‘’ #(a) ->’a’ #(a b c) -> ‘a, b, c’

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#(a b c)do: [:each | Transcript show: each printString]separatedBy: [Transcript show: ‘,’]

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#(a b c)do: [:each | Transcript show: each printString]separatedBy: [Transcript show: ‘,’]

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Messages Sequencemessage1 .message2 .message3

. is a separator, not a terminator

| macNode pcNode node1 printerNode |macNode := Workstation withName: #mac.Transcript cr.Transcript show: 1 printString.Transcript cr.Transcript show: 2 printString

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Multiple messages to an objects ;

To send multiple messages to the same object

Transcript show: 1 printString.

Transcript cr

is equivalent to:

Transcript show: 1 printString ; cr

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Hints ...

x isNil ifTrue: [...]

x includes: 3 ifTrue: [...]

is read as the message includes:ifTrue:

(x includes: 3) ifTrue: [...]

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Smalltalk is funPure simple powerful

www.seaside.st(www.dabbledb.com)www.pharo-project.org