Ruby

ESA2011/2012

AdamBellouma.s.z.belloum@uva.nl

MaterialPreparedbyEelcoSchatborn

ESA:Ruby

•  Today:1.RubyintroducDon2.BasicRuby:types,variables,statements,...

3.ObjectOrientedRuby:class,modules,…4.DocumentaDon

IntroducDontoRuby

•  RubywascreatedbyYukihiro•  Matsumoto()a.k.a.“Matz”•  Introducedin1994•  OfficiallyreleasedbyMatsumotoin1995.•  “Ruby”wasnamedasagemstoneasajoke...•  TheTIOBEindex,whichmeasuresthegrowthof

programminglanguages,ranksRubyas#9amongprogramminglanguagesworldwide(2006)

“tryingtomakeRubynatural,notsimple,”“Rubyissimpleinappearance,butisverycomplex

inside,justlikeourhumanbody”

IntroducDontoRuby

•  Rubyis"aninterpretedscrip9nglanguageforquickandeasyobject‐orientedprogramming"‐‐whatdoesthismean?

•  interpretedscrip+nglanguage:–  abilitytomakeoperaDngsystemcallsdirectly–  powerfulstringopera9onsandregularexpressions–  immediatefeedbackduringdevelopment

h`p://www.rubyist.net/~slagell/ruby/index.html

IntroducDontoRuby

•  Rubyis"aninterpretedscripDnglanguageforquickandeasyobject‐orientedprogramming"‐‐whatdoesthismean?

•  quickandeasy:–  variabledeclaraDonsareunnecessary–  variablesarenottyped–  syntaxissimpleandconsistent

– memorymanagementisautomaDc

h`p://www.rubyist.net/~slagell/ruby/index.html

IntroducDontoRuby

•  Rubyis"aninterpretedscripDnglanguageforquickandeasyobject‐orientedprogramming"‐‐whatdoesthismean?

•  objectorientedprogramming:–  everythingisanobject–  classes,methods,inheritance,etc.

–  "mixin"funcDonalitybymodule–  iteratorsandclosures(h`p://www.arDma.com/intv/closures.html)

h`p://www.rubyist.net/~slagell/ruby/index.html

IntroducDontoRuby

•  Rubyis"aninterpretedscripDnglanguageforquickandeasyobject‐orientedprogramming"‐‐whatdoesthismean?

•  also:–  mulDpleprecisionnumbers–  convenientexcep9onprocessing–  dynamicloading–  threadingsupport.

h`p://www.rubyist.net/~slagell/ruby/index.html

Ruby,PerlandPython

•  Designgoals–  Expressivelikeperlbutbe`erObject‐OrientaDon–  LikepythonbutimplemenDngtrueObject‐OrientaDon

–  Noprimi9vetypes,everythingisanobject/class–  Fullyscriptable

SimpleExample

#!/usr/bin/ruby

def power(x,n) result = 1

x = x*x n = n/2

end

return result end

RubyBasics

•  NormalmethodforscripDngusing#!/usr/bin/ruby

•  irbisaninteracDverubyinterpreter–  Youcaninterpretsinglelinesofcode–  Goodforsimplecheckinganddebugging

•  YoucandocumentRubycodeusingtheRDocsystem–  ThedocumentaDonisinsidethesourcefile–  Itcanbeextractedusingri–  TofindthedocumentaDonforaclasstype ri classname atthecommandprompt

Numbers

Simplenumbers:–  binary,startwith0b:0b1100,‐0b10001,0b11111111...–  decimal:12,‐17,255...–  octal,startwith0:015,‐023,0777...–  hexadecimal,startwith0x:0xc,‐0x11,0xff,...–  floaDngpointnumbers: “oneandaquarter":1.25

–  scienDficnotaDon:“7.25Dmes10tothe45thpower":7.25e45.

Butalsomatricesandcomplexnumbersusingseparatemodules

Strings(1)•  Tocreatestringliterals,enclosetheminsingle,ordoublequotes.

•  Examples: 'Hello Class of 2007' "Ruby is shiny”

•  Thesametypeofquoteusedtostartthestringmustbeusedtoterminateit.

•  Youcanhaveyourowndelimitersusing%%q!"I said 'nuts'", I said! # %q‐appliesthesimplequoterules %Q(It's like a " string,\n \\n is a newline) # %Qappliesthedoublequoterules

If you use () {} [] as delimiter you can use these delimiters as a text as long as they are in pairs

Strings(2)

•  Escapesequencesforsinglequoted(')strings: only \\ and \’

•  Fordoublequoted(‘”’)strings: \a, \b, \e, \f, \n, \r, \s, \t,

•  Youcanembedrubycodeintoadoublequotedstringusing#{. . . }:

"Seconds/day: #{24*60*60}” Seconds/day: 86400

Strings(3)

•  IntermiGantsingleanddoublequotedstringsareconcatenatedtooneobject: "'Well'" ', he said, ' '"How are you?"’ 'Well', he said, "How Are You?”

•  YoucanconstructamulDlinestringusinga“heredocument”:

string = <<END_OF_STRING The Body of the string is the input lines up to one ending with the same text that followed the '<<' END_OF_STRING

VariablesandConstants

•  Rubyvariablesandconstantsholdreferencestoobjects.

–  Theobjectdecidesthetype,notthevariable–  Reassignmentcanchangethetypeofthevariable

•  Namingisasfollows:Constantsstartwitha[A-Z],theconvenDonisto

writeallcapswithunderscores

localvariables startwitha[a-z\_] globalvariablesstartwitha`$' instancevariablesstartwitha`@’ classvariables startwith`@@’

Predefinedvariables

•  Mostpredefinedvariablescomefromperl

•  Therearepredefinedvariablesfor:Input/Output($_, $., …) Pa`ernMatching($=, $1 to $9, …) ExecuDonEnvironment(Ruby specific) ($0, $”, …) ExcepDoninformaDon($!, $@) Standardobjects(true, false, ARGV, …) globalConstants(STDIN, STDOUT, …)

http://www.softlab.ntua.gr/facilities/documentation/unix/ruby-man-1.4/variable.html#equal

Stringvariables

•  Stringvariablesareindexedlikelists,starDngat0•  Youcanusethemusingtheindexoperator`[i]' a = "Hello World" b = a[4] # b = o

•  Substringscanbeusedbypairnumbers:`[start,count]' c = a[0,6] # c = "Hello " d = a[7,4] # d = "orld"

e = a[3,5] # e = "lo Wo”

•  Rangescanalsobeusedtospecifyindices.

Ranges

•  Constructrangesofnumbersorcharacters

•  UsedoubledotnotaDonforinclusiverangecreaDon: 1..5 [1, 2, 3, 4, 5]

•  UsetripledotnotaDonforexclusiverangecreaDon: 1...5 [1, 2, 3, 4]

Exampleforstringvariables: a = "Hello World"

c = a[0..5] # c = "Hello " d = a[7..10] # d = "orld"

e = a[3...9] # e = ?

Arrays

•  Arraysarearbitrarylistsofobjects•  CreateanArrayusing[]: names = [“Fred”,2,"Flintstone”] •  Theytooareindexed: a = names[1] # a is now 2

names[0] = “Wilma” # names is changed

•  Usingarange: names[1..2] [ 2, "Flintstone" ]

Hashes(1)

•  Ahashcontainsobjectsindexedbykeys.•  Anyobjectcanbeusedasakeyorvalue,but...•  Createahashbyenclosing`key => value’combinaDonsincurlybraces(`{...}'):

a = { "username" => "xenos", "home" => "/home/xenos”,

"uid" => 500

}

Hashes(2)

•  Accessanyvalueusingit'skey:u = a["username"] # Returns "xenos" d = a["home"] # Returns "/home/xenos”

•  Toinsertormodifyobjects,youassignavaluetoakey‐indexedname.a["username"] = "trixie"

a["home"] = "/home/trixie" a["shell"] = "/usr/bin/tcsh"

Hashes(3)

•  Hashmembershipistestedwithseveralmethods:has_key?,has_value?,keys,values

a.has_key? "username” # return True a.has_value? "trixie” # return false a.keys # ["xenos", 500, “/usr/bin/tcsh”, "/home/xenos”]

a.values # ["username", "uid", "shell", "home"]

Expressions

•  Singletermsare:–  Literals(numbers,strings,arrays,hashes,ranges,symbols,RE's)–  Shellcommands,usingbackquotes:`‘...‘`

files=‘ls*‘–  Variableorconstantreferences

•  Expressionblocksaredenotedbybegin/do . . . end •  Theusualoperators:

+, -, *, /, %, **, !, …

•  Mostoperatorsareimplementedasmethods(may be overridden)

Assignment

•  Usingparallelassignmentyoucanforegotouseoftemporaryvariables: a = 1

b = 2 temp = a a = b b = temp

Usingparallelassignment: a, b = b, a

ComparisonOperators

== Testforequalvalue

=== Comparisonoperatorforthecasestatement<=> Generalcomparisonoperator(returns‐1,0,1)<,<=,>,>=Normalcomparisonoperators

=~ Regularexpressionmatcheql? Checksfortypeandvalueequalityequal?ChecksforObjectIDequality

Flowcontrol

•  Codeblocksaredenotedby{...}ordo...endblocks

•  CodeblockscanstartwithanargumentlistbetweenverDcalbars:|…|

•  #!/usr/bin/rubypresidents=["Ford","Carter","Reagan","Bush1","Clinton”]presidents.each{|prez|putsprez}

•  Flowcontrolcanbeexertedusingloopingorcondi9onalstatements.

LoopingStatements(1)•  Thestandardconstructsarepresent:

while condition body end

•  Usingabegin...endblockthesyntaxcanbereversed:

begin body end while condition

until condition body

end

begin body

end until condition

LoopingStatements(2)

•  IteraDngoverthemembersofasequencecontaininganytypeofobject.

for i in [1,2,"three", 4, 5,'eleven', 7 ] print i," "

end •  Youcanalsousearange: for i in 1..10 print i," " end

LoopingStatements(3)

•  MoststandardobjecttypesalsoprovideiteratormethodsExamplesfornumbers:3.times do print "Hi! " end

0.upto(93) do print "Ha! " end

•  Forarrays/files/etceterathereare:obj.each, obj.foreach, . . .

CondiDonalstatements(1)

•  ifandunlessstatements:if test [ : | then] body

elsif test [ : | then ] body else body

end

•  Youcanalsousethemonexpressionsasmodifiers:expression if test expression unless test

unless test [ : | then ] body

else body

end

CondiDonalStatements(2)

•  casestatementcompareseachwhenclausetoatargetandexecutesthefirstmatch

case target when comparison [: | then] body when comparison [: | then] body . . . [else body ] end

h`p://ilikestu~log.com/2008/04/15/how‐to‐write‐case‐switch‐statements‐in‐ruby/

RegularExpressions

•  RegularexpressionsareanobjectoftypeRegexp•  Theycanbecreatedusing:

/ pattern / [options] %r{ pattern } [options] Regexp.new(' pattern ' [ , options] )

•  MoststandardopDonsandpa`ernsareavailable•  FormoreinformaDonseethedocumentaDon

•  r1 = Regexp.new('^a-z+:\\s+\w+') #=> /^a-z+:\s+\w+/

a = "HELLO” case a

when /^[a-z]*$/; print "Lower case\n”

when /^[A-Z]*$/; print "Upper case\n” else; print "Mixed case\n”

end

Methods(1)

•  Amethodcanhavearguments,theyarepassedtotheblockasanarray

•  Amethodwillreturntheresultofthelastexecutedexpressionintheblockasthereturnvalue

•  Thereturnexpressionwillexitthemethodimmediatelygivingitsargumentasareturnvalue

Methods(2)•  AsimplemethoddefiniDonisasfollows:

def sayhi(name) print "Hi", name

End

•  AdefiniDonusingpre‐ini9alizedarguments:

def options(a=99, b=a+1) [ a, b ] end

options [99, 100] options 1 [1, 2] options 2, 4 [2, 4]

Methods(3)

•  supermethodisaspecialmethodforobjects–  ItexecutesthefuncDonofthesamenameintheparentobject–  toensurecrea9onorini9aliza9onofparentobjects

•  superwithnoarguments–  Rubysendsamessagetotheparentofthecurrentobject,–  toinvokeamethodofthesamenameasthemethodinvokingsuper.–  ItautomaDcallyforwardstheargumentsthatwerepassedtothe

methodfromwhichit'scalled.•  super()withanemptyargumentlist

–  itsendsnoargumentstothehigher‐upmethod,evenifargumentswerepassedtothecurrentmethod.

•  super(a,b,c)withspecificarguments–  itsendsexactlythosearguments.

Classes(1)

•  ArubyclassisanextensionoftheclassClass•  Classnamesstartwitha[A-Z] •  Classescreateanewnamespace•  Classescanbenested,buttheywillnotbemadeglobal,

soinstanDaDonrequiresthefullyqualifiedclassname•  AsimpleexampledefiniDon:

class MyClass CONST = 12345 def f 'hello world' end end

Classes(2)

•  Createaninstanceobjectfromaclassasfollows: obj = MyClass.new •  TheclassClassdefinesamethodnewwhichisresponsiblefor

thecreaDonofanobjectoftheclass

–  Thenewmethodmustcallthesupermethodtoallowtheparentclasstobeallocated,otherwisenoobjectsofthatclasscanbecreated.

•  TheclassClassalsodefinesthemethodinitialize,whichwillbeinvokedinanewlycreatedobject,itwillreceivetheargumentspassedtonew.

–  TheinitializemethodmustalsocallsuperiftheparentobjectistobeproperlyiniDalized

Classes(3)

•  TouseamethodfromanobjectuseadotnotaDon:obj.f

•  ToretrieveaconstantfromanobjectusethedoublecolonnotaDon:obj::CONST

•  Examples: obj.f # hello world

obj::CONST # 12345

Classes(4)

Classvariables•  classvariablesarevariablessharedbetweenallobjects

ofaclass

class Song @@plays = 0 def play @@plays += 1 "This song: Total #@@plays plays." end end

Classes(5)

Classmethods‐objectmethodsvs.classmethods‐aclassmayneedtoprovidemethodsthatworkwithoutbeingDedtoanyparDcularobject.ForexampleMyClass.new.

•  Example

class Example def instMeth # instance method end def Example.classMeth # class method end end

Modules(1)

•  Modulesareawayofgroupingtogethermethods,classes,andconstants.Modulesgiveyoutwomajorbenefits.–  Modulesprovideanamespaceandpreventnameclashes.–  Modulesimplementthemixinfacility.

•  ARubyModuleisbasicallyaclassthatcannotbeinstan9ated

•  MulDplemodulesmaybecreatedinasinglesourcefile•  UsethedefiniDonsinamoduleinthesamewayyou

wouldan(instanDated)object•  Aredefini9onofamoduleresultsinoverloadingthat

module

Modules(2)

•  AmoduledefiniDon: CONST = "outer" module A CONST = 1 def A.method CONST + 1 end end

•  QuesDons: CONST "outer" A::CONST 1 A.method 2

Modules(3)

•  AmoduledefiniDonwithscopeinheritance:CONST = "outer" module B def B.method CONST + "scope"

end end

•  QuesDon: B.method "outerscope”

Modules(4)

•  ModulescanbeincludedinthedefiniDonofanothermoduleorclassuse:include <module‐name>

require <modules-name>

•  Theincludingmodulewillhaveaccesstoallconstants,variables,methodsetceterafromtheincludedmodule

•  Aclassmayalsoincludeamodule–  Themodulewillbetreatedasasuperclassfortheclass

–  Themodulecanalsocontainanini9alizemethod

Modules(5)

module SillyModule def hello

"Hello." end end

Question s.hello ”Hello”

class SillyClass include SillyModule

End

s = SillyClass.new

IncludingSourcefiles

•  IncludeRubysourcefilesintoaprogramusingloadorrequire

Load loadsthereferencedfileeachDmeitiscalledUsefulfor(re)loadingsourcecodegeneratedatrun‐Dmerequire loadsthereferencedfileonlyoncerequireisastatement,itcanbeuseanywherestatements areallowed.Forinstancefromwithinanifstatement.

•  Localvariablesinaloadedfilearenotpropagatedtothescopeoftheloadingfile

DocumentaDon

•  BOOKS!,theyareinthebackoftheclassroom...

•  Usetheweb,therearegoodwebsitesonruby•  Checkh`p://www.ruby‐lang.org/forhelp.•  h`p://www.ruby‐doc.org/docs/ruby‐doc‐bundle/index.html

•  “ProgrammingRuby",canbefoundonlineviaabovelink

PlayAround

•  writeafunc9onfacttocomputefactorials.–  ThemathemaDcaldefiniDonofnfactorialis: n!=1(whenn==0)=n*(n‐1)!(otherwise)

•  writeasimplerubyprogwithcasestatementwheregivenamodelofacaritprintsthebrand

•  writeasimplerubyprogwitharrays,printtheelementofthearray,removeelements,prependelements–  Hint:Rubyarrayshavemethodsshi�,unshi�,push,andpop)

•  writeasimplerubywithcontrolstatementif.WhengivendemocratsitprintsthenamesofdemocratspresidentsinUSsince1976,sameforrepublicans

PlayAround

•  writeaclassDecadeandamoduleWeektoprintthenumberofweeksinamonth,ayear,andthenumberofdaysinadecade(includetheWeekmoduleintheClassDecade)

– 

•  writeaclasswithrunDmeExcep9onhandling.IftheageofagivenpaDentisbellowacertainage,itgenerateanexcepDon.–  Hints:useraisetogeneratetheexp,andrescuetocatchit

PlayAround

•  writeafunc9onfacttocomputefactorials.–  ThemathemaDcaldefiniDonofnfactorialis: n!=1(whenn==0)=n*(n‐1)!(otherwise)

# Program to find the factorial of a number # Save this as fact.rb def fact(n) if n == 0 1 else n * fact(n-1) end

end puts fact(ARGV[0].to_i)

PlayAround

•  writeasimplerubyprogwithcasestatementwheregivenamodelofacaritprintsthebrandcar = "Patriot” manufacturer = case car when "Focus": "Ford" when "Navigator" then "Lincoln" when "Camry" then "Toyota" when "Civic" then "Honda" when "Patriot": "Jeep" when "Jetta" ; "VW" when "Ceyene” "Porsche” when "520i" then "BMW” else "Unknown" end puts "The " + car + " is made by " + manufacturer

PlayAround

•  writeasimplerubyprogwitharrays,printtheelementofthearrayremoveelements,prependelements

•  Hint:Rubyarrayshavemethodsshi�,unshi�,push,andpop)

#!/usr/bin/ruby presidents = ["Ford", "Carter", "Reagan", "Bush1", "Clinton", "Bush2"] presidents.each { |i| print i, "\n"}

#Remove 3 elements from the array #!/usr/bin/ruby

presidents = ["Ford", "Carter", "Reagan", "Bush1", "Clinton", "Bush2"]

presidents.pop presidents.pop presidents.pop presidents.each { |i| print i, "\n"}

PlayAround

•  writeasimplerubyprogwitharrays,printtheelementofthearray,removeelements,andprependelements

•  Hint:Rubyarrayshavemethodsshi�,unshi�,push,andpop)

#!/usr/bin/ruby presidents = ["Ford", "Carter", "Reagan", "Bush1", "Clinton", "Bush2"] presidents.each { |i| print i, "\n"}

#Prepend 3 elements to the array #!/usr/bin/ruby

presidents = ["Ford", "Carter", "Reagan", "Bush1", "Clinton", "Bush2”] presidents.unshift("Nixon") presidents.unshift("Johnson") presidents.unshift("Kennedy") presidents.each { |i| print i, "\n"}

PlayAround

•  writeasimplerubywithcontrolstatementif.WhengivendemocratsitprintsthenamesofdemocratspresidentsinUSsince1976,sameforrepublicans

#!/usr/bin/ruby democrats = ["Carter", "Clinton”]

republicans = ["Ford", "Reagan", "Bush1", "Bush2”] party = ARGV[0]

if party == nil print "Argument must be \"democrats\" or \"republicans\"\n" elsif party == "democrats" democrats.each { |i| print i, " "} print "\n" elsif party == "republicans" republicans.each { |i| print i, " "} print "\n" else print "All presidents since 1976 were either Democrats or Republicans\n" end

PlayAround

•  writeaclassDecadeandamoduleWeektoprintthenumberofweeksinamonth,ayear,andthenumberofdaysinadecade(includetheWeekmoduleintheClassDecade)

#!/usr/bin/ruby require "Week” class Decade

include Week no_of_yrs=10 def no_of_months puts Week::FIRST_DAY number=10*12 puts number end

end

!/usr/bin/ruby module Week FIRST_DAY = "Sunday"

def Week.weeks_in_month puts “four weeks in a month"

end

def Week.weeks_in_year

puts “52 weeks in a year"

end end

PlayAround

•  writeaclassDecadeandamoduleWeektoprintthenumberofweeksinamonth,ayear,andthenumberofdaysinadecade(includetheWeekmoduleintheClassDecade)

#!/usr/bin/ruby require "Week” class Decade

include Week no_of_yrs=10 def no_of_months puts Week::FIRST_DAY number=10*12 puts number end

end

d1=Decade.new puts Week::FIRST_DAY Week.weeks_in_month Week.weeks_in_year d1.no_of_months

PlayAround•  writeaclasswithrunDmeExcep9onhandling.IftheageofagivenpaDentis

bellowacertainage,itgenerateanexcepDon.•  Hints:useraisetogeneratetheexp,andrescuetocatchit

class MedicareEligibilityException < RuntimeError def initialize(name, age) @name = name @age = age end def getName return @name end def getAge return @age end end … next page …

PlayAround

def writeToDatabase(name, age) # This is a stub routine

print "Diagnostic: ”,name, ”,age ", age, " is signed up.\n"

end def signHimUp(name, age)

if age >= 65 : writeToDatabase(name, age) else

myException =

MedicareEligibilityException.new(name, age) raise myException , "Must be 65 or older for Medicare", caller

End

end … next page …

PlayAround

# Main routine begin signHimUp("Oliver Oldster", 78)

signHimUp("Billy Boywonder", 18) signHimUp("Cindy Centurinarian", 100)

signHimUp("Bob Baby", 2)

rescue MedicareEligibilityException => elg print elg.getName, " is ", elg.getAge, ",

which is too young.\n" print "You must obtain an exception from

your supervisor. ", elg, "\n” end print "This happens after signHimUp was called.\n"

PlayAround•  writeasimpleprogwithtwoclassesMammalandcatthecatClass

extendsMammal.• 

# class Mammal def breathe puts "inhale and exhale" end end

class Cat<Mammal def speak puts "Meow" end end

tama = Cat.new tama.breathe tama.speak

PlayAround•  writeaprogforreducedfarforthetrain(3ClassesTraveler,Student,

Honest,bothStudentandHonestinheritance

class Traveler def identify puts "I'm a Traveler." end def train_toll(age) if age < 12 puts "Reduced fare."; else puts "Normal fare."; end end end

PlayAround

class Student<Traveler def identify puts "I'm a student." end end

class Honest<Traveler def train_toll(age) super(age) # pass the argument we were given end

end Traveler.new.identify Student1.new.identify Honest.new.train_toll(25)

Assignment

WewillbecreaDnganAlumnidatabasesystem.1.createaclass'alumnus'tostoreasinglepersonor

alumnusin.Createamethodforseparatelyaddingfriends(byreferencetoanexisDngalumnusobject!)

2.testtheclassbycreaDngagroupofalumniwhoarefriends.

3.Notallalumnihavetobedirectfriends,youcanalsohaveacquaintances.Theyarefriendsofyourfriendsthatarenotyourdirectfriend.

So:adistanceof1isyourfriend,adistanceof2isanacquaintanceandmorethan2isunknown.

Assignment

4.createaclassthatprintsinformaDonaboutasinglealumnus4.1createamethodforprinDngallfriendsofthealumnusbyname4.2createamethodforprinDngallacquaintancesofthealumnusby

name4.3createamethodthatprintsALLconnectedalumniatanydistancefor

thegivenalumnus.ForeachconnecDonprintthedistancenumber,thetypeofrelaDonandthealumnithroughwhichtheyareconnected

so:2:acquaintance:eelco‐>jarno‐>karstimpliesthateelcoknowskarstthroughjarno,meaningjarnoisafriendandkarstisanacquaintance.

NotethattherecanbemulDplewaysthateelcoknowskarst,alwayschoosetheshortestroute,andnevershowaconnecDontwice