Listoflectures
IntroductionandFunctionalProgramming
ImperativeProgrammingandDataStructures
3
Environment
4
Evaluation
5
ObjectOrientedProgrammingandtypesystem
6
Macrosand
7
VirtualMachinesandBytecode
8
GarbageCollectionandNativeCode
9
DistributedComputing
10
Logic
11
Guestlecture
12
Summary
1
TDDA69DataandProgramStructure
ObjectOrientedProgramming
andtypesystem
CyrilleBerger
2
2/54
Lecturegoal
Lecturecontent
Object-orientedandtype
ObjectOrientedProgramming
conceptsandconscequenceforprogram
interpretation
Object-OrientedConcepts
Implementation
Revisitingthevisitorpattern
Exceptions
Type
3/54
4/54
ProgramOrganizingTechniques
Non-structuredProgramming
StructuredProgramming
ObjectOrientedProgramming
ModularProgramming
Object-OrientedProgramming
6
Non-structuredProgramming
ProceduralProgramming
Themainprogramdirectlyoperates
onglobadata
Combineasequenceofstatementsinto
aprocedurewithcallsandreturns
Themainprogramcoordinatescallsto
proceduresandhandsoverappropriatedataas
Program
mainprogram/data
Program
mainprogram/data
Impracticalwhentheprogramgets
sufficientlylarge
Thesamestatementsequencemust
becopiedifitisneededseveraltimes
Procedure1
Procedure2
Procedure3
Tasksareacollectionofstates,structures
andprocedures
7
8
ModularProgramming
LimitationsofStructuredandModularProgramming
Unrestrictedaccesstoglobal
Proceduresofacommonfunctionalityaregrouped
togetherintoseparatemodules.
Themainprogramcoordinatescallstoproceduresin
separatemodulesandhandsoverdataasparameters.
Globaldata1
Program
Procedure1
mainprogram/data
Module1data+data1
Procedure1
Procedure2
Globaldata2
Procedure2
Procedure3
Globaldata3
Procedure4
Attributesandbehaviorsare
seperated
Not
Module2data+data2
Procedure3
9
10
WhatisObject-OrientedProgramming?
Object-OrientedConcepts
Amodelingtechnique
Itisanaturaltechnique
Theworldismadeofobjects:house,tree,car,
computer...
Allowtodescribeaprogram
beforeitiswritten
12
WhatisanObject?
Object-OrientedConcepts
Class
Inheritance
Encapsulation
Polymorphism
Real-worldobjectsarecomposed
ofattributesandbehaviors
Attributes:color,size,...
Behaviors:accelerate,brake,...
Program
Attributesarestates/variables
Behaviorsarefunctions
13
14
Class
ClassCar
classCar:
Anobjectisaspecificinstance(iethiscar,
thiscomputer...)
Aclassisatypeofobject(ieacar,a
computer...)
attributes:
colorcanbered,green,blue...
speedfrom0tomax_speed
max_speedandmax_accelerationareconstant
functions:
Itisablueprintofobject
Theclassdefines:
accelerateincreasespeedwithmax_acceleration
brakedecreasespeedwithmax_acceleration
Thedefaultsetofvariables
Thedefaultsetoffunctions
Aninitialisationfunction(calledconstructor
object:
red_audi:={color:'red',max_speed:200,
max_acceleration:10}
blue_volvo:={color:'blue',max_speed:180,
max_acceleration:7}
Theobjectisaninstanceofaclass
Itpointstoaspecificmemorylocationwiththeactualvalues
forvariables
15
16
Inheritance
InheritancefromtheclassCar
classCar:color,speed,
max_speedandmax_acceleration
classAudi:classCarwith
max_speed:=200and
max_acceleration:=10
classVolvo:classCarwith
max_speed:=180and
max_acceleration:=7
Someclasseshavecommonpart
Audiisacar,Volvoisacar,butVolvoandAudi
aretwodifferenttypeofcars
Inheritanceallowstodefineaclass
intermofanothersuper-class
Sub-classes
canaddnewvariablesandfunctions
overridevariablesandfunctionsfromthe
super-class
17
Encapsulation
18
Polymorphism
polymorphismistheabilitytoappear
inmanyforms
Itistheabilitytocallafunctiononan
objectthatwillexecutedifferentcode
fordifferentobjects
Forexample,ashapeclasswithan
areafunctionandtriangle,square...
Itisonewayofcreatinggenericcode
Encapsulationistheabilityto
hidevariables
Threecommonlevelsof
Private:onlyaccessibletotheobject
Protected:onlyaccessibletotheobjectandthrough
inheritance
Public:accessibletotheworld
19
20
TheadvantagesofObject-OrientedProgramming
Codereusability
Codecansharedinthesuperclass
Polymorphismallowtodefineinterfaces
Inheritenceclarifiesthe
relationshipamongprogram
elements
Encapsulationallowmodularity
andcontrolonaccessto
variables
Implementation
21
ImplementingObject-OrientedProgramming
(Almost)anyimperative
programminglanguagecanbe
madetosupportobject-oriented
programming
Definingmembers:variables
Allyouneedisa
InJavaScript/
obj={value:1.0,name:'someobject'}
console.log(obj.value)
console.log(obj['value'])
Forinstance,firstC++compilerwascompiling
toCandmanyobjectsystemshavebeen
addedtoC
23
In
classTest
def__init__(self):
self.value=1.0
self.name='someobject'
obj=Test()
print(obj.value)
console.log(obj.__dict__['value'])
24
Definingmembers:functions
Allmostallyouneedistosave
Whataboutclasses?
Withdictionnarywehaveobjects
Foraclass,allweneedisaconstructor
obj={value:1.0,dosomething:function(){return42;}
Buthowtoaccessthevariables
Youeitherneedtopassapointerto
theobject
functioncreate_car(self,color,max_speed,max_acceleration):
self.color=color
self.speed=0.0
self.max_speed=max_speed
self.max_acceleration=max_acceleration
self.accelerate=function(){self.speed=Math.min(self.max_speed,
self.speed+self.max_acceleration)}
self.decelerate=function(){self.speed=Math.max(0,self.speedself.max_acceleration)}
Implicitely,likeinJavaScript/ECMAScript:
obj={value:1.0,getValue:function(){returnthis.value;}}
Explicitely,likeinPython:
classTest
def__init__(self):
self.value=1.0
defgetValue(self):
returnself.value
Forinheritance,allweneedistocallthesuperclass
constructor
functioncreate_audi(self,color):
create_audi(self,color,200,10)
25
26
Whataboutencapsulation?
ClassinJavaScript/ECMAScript
functionCar(color,max_speed,max_acceleration)
{
this.color=color
...
}
Car.prototype.accelerate=function(){self.speed=
Math.min(self.max_speed,self.speed+self.max_acceleration)
}
Car.prototype.decelerate=...
functionAudi(color)
{
Car.call(color,200,10)
}
Audi.prototype=Object.create(Car.prototype)
red_audi=newAudi('red')
red_audi.accelerate()
(Ab)usingenvironment
functionCar(color,max_speed,max_acceleration)
{
this.getColor=function(){returncolor}
...
}
Andforprotected
functionCar(color,max_speed,
max_acceleration,protected={})
{
protected.color=color
...
}
functionAudi(color)
{
varprotected={}
Car.call(color,200,10,protected)
this.getColor=function(){returnprotected.color}
}
Audi.prototype=Object.create(Car.prototype)
27
28
Whataboutpolymorphism?
Justoverwritefunctioninthechildclass
functionShape()
{
this.area=function(){throw'Error';}
}
functionSquare(width,height)
{
Shape.call(this)
this.area=function(){returnwidth*height}
}
Square.prototype=Object.create(Shape.prototype)
Revisitingthevisitorpattern
29
Example
Object-OrientedAbstractSyntaxTree
['+'[1
['*'[4
['/'[5
['+'[23]
]]]]]]]
Addition.new(1,
Multiplication.new(4,
Division.new(5,
Addition.new(2,3))))
AnValueclass
classValue:
def__init__(self,
value):
self.value=value
AnOperatorclass
classOperator:
def__init__(self,a,
b):
self.a=a
self.b=b
Anadditionclass
class
Addition(Operator):
def__init__(self,a,b):
...super().__init__(a,b)
31
32
Visitor
defevaluate(node):
ifnotisinstance(node,list):
returnnode
elifnode[0]=='+':
returnevaluate(node[1][0])
+evaluate(node[1][1])
elifnode[0]=='-':
returnevaluate(node[1][0])
-evaluate(node[1][1])
elifnode[0]=='*':
returnevaluate(node[1][0])
*evaluate(node[1][1])
elifarray[0]=='/':
returnevaluate(node[1][0])
/evaluate(node[1][1])
else:
raiseError()
OrientedObjectvisitor(1/2)
classVisitor:
defvisitValue(self,node):
returnnode.value
defvisitAddition(self,node):
returnnode.a.accept(self)+
node.b.accept(self)
defvisitSubstraction(self,node):
returnnode.a.accept(self)-node.b.accept(self)
defvisitMultiplication(self,node):
returnnode.a.accept(self)*node.b.accept(self)
defvisitDivision(self,node):
defevaluate(node):
ifisinstance(node,Value):
returnnode.value
elifisinstance(node,Addition):
returnevaluate(node.a)
+evaluate(node.b)
elifisinstance(node,Substraction):
returnevaluate(node.a)
-evaluate(node.b)
elifisinstance(node,Multiplication):
returnevaluate(node.a)
*evaluate(node.b)
elifisinstance(node,Division):
returnevaluate(node.a)
/evaluate(node.b)
else:
raiseError()
33
OrientedObjectvisitor(2/2)
34
Whyusethevisitorpatternatall?
classValue:
...
defaccept(self,visitor):
return
visitor.visitValue(self)
classAddition:
...
defaccept(self,visitor):
returnvisitor.visitAddition(self)
Easywaytoextend
Foraninterpreted:
Avisitorforevaluating
Avisitortoconverttoadifferentprogramming
language
Avisitortogeneratebytecode
...
35
36
SoftwareExceptions
Exceptionsareeventsthataffect
thecontrolflowofaprogram.
Anexceptionallowstoreturnfrom
afunctionorastatmentatany
point,withanytypeandonany
numberoflevels.
Exceptionneedtobecaught.
Exceptions
38
Whatareexceptionsusedfor?
Controlflowandexceptions
www.govote.at217195
try:
a()
rescueException:
print('rescued')
defa():
b()
print('Nevercalled')
defb():
throwException()
39
40
Exceptionforerrorhandling
Exceptionforexitingadoubleloop
Mostcommonuseofexceptionis
forerrorhandling
Moreconvenientthanreturninga
value(whichisnotpossibleina
constructor)
try:
foriinrange(0,10):
forjinrange(0,40):
ifi*j==300:
throwException('doublebreak')
except:
pass
41
Breakandreturnstatement
42
Usingexceptionforbreakandreturn
Instead,letsuse
Howtoimplementthe'break'and'return'statement?
WhileStatement.new(...,[...BreakStatement.new])
Usingareturnvalue?
classEvalVisitor:
defvisitBreakStatement(self,node):
throwBreakException()
defvisitWhileStatement(self,node):
try:
while(node.condition.accept(self)):
visitChildren(node)
rescueBreakException:
pass
defvisitChildren(self,node):
for(childinnode.children):
child.accept(self)
classEvalVisitor:
defvisitBreakStatement(self,node):
returnfalse
defvisitWhileStatement(self,node):
while(node.condition.accept(self)):
ifnotvisitChildren(node):
break;
returntrue
defvisitChildren(self,node):
for(childinnode.children):
if(notchild.accept(self)
returnfalse
returntrue
Verysimilartoerrorchecking
43
44
Andhowtoimplementexceptionintheinterpreter?
Usingexceptions...
classEvalVisitor:
defvisitThrowStatement(self,node):
throwInterpretedException(node.exceptionType)
defvisitTryCatchStatement(self,node):
try:
visitChildren(node.body)
exceptInterpretedExceptionasie:
ifie.type==node.exceptionType:
visitChildren(node.catch)
else:
throwie
Typesystem
45
Type-Checking
Whatisatypesystem?
Atypesystemdefineshowatype
isassociatedtoavariable
Variablesarestoredasbits
inmemory
Atypegivemeaningtoaset
ofbits
Inaprogram,avalueis
associatedtoatleastone
type
Static-typechecking
Typesarecheckedatcompilationfromstatic
analysis
Usuallyvariableshaveasingletype
Polymorphismallowsfordynamicity
Supportfromdowncasting
Dynamic-typechecking
Typesarecheckedatruntime
Thetypeofavariablecanchange
Unchecked
Example:machinecode
47
48
Static-typechecking
Static-typevsDynamic-type
Allowforoptimization
Trade-off
Thenumberofactualerrorsfound
throughstatictypingisdebatable
Dynamictypingallowsfor
fasterdevelopmentandfaster
compilation
Noneedtocheckfortypesatruntime
Programverification
Canworkbetterthanunit-tests
if(almostalwaystrue){/*validcode*/}
else{/*typeinvalidcode*/}
Butdowncastingcannotbeverifiedwithstatic
checking
49
Implementingstatic-typing
50
Implementingdynamic-typing
classEvalVisitor:
defdoArithmetic(self,op,node):
a=node.a.accept(self)
b=node.b.accept(self)
if(a.type==b.type):
returnop(a,b)
elif(a.type.canConvert(b.type)):
returnop(a.convert(b.type),b)
elif(b.type.canConvert(a.type)):
returnop(a,b.convert(a.type))
else:
throwExecutionError('Invalidtypes')
defvisitAddition(node):
returnself.doArithmetic(operators.add,
node)
WithanASTvisitor!
Insteadofreturningavalue,returnatype
classStaticTypeCheckerVisitor:
defvisitValue(self,node):
returnnode.type
defcheckArithmetic(self,typeA,typeB):
if(typeA==typeB):
returntypeA
elif(typeA.canConvert(typeB)):
returntypeB
elif(typeB.canConvert(typeA)):
returntypeA
else:
throwCompilationError('Invalidtypes')
defvisitAddition(self,node):
returnself.checkArithmetic(node.a.accept(self),
node.b.accept(self)
defvisitAssignment(self,node):
typeVariable=
environment.getVariable(node.variableName).type
typeValue=node.value.accept(self)
if(typeVariable!=typeValue
and!typeValue.canConvert(typeVariable)):
throwCompilationError('Invalidtypes')
returntypeVariable
51
52
StrongvsWeaktyping
Conclusion
Alanguageissaidtobestrongly
typedwhenitrequiresexplicitely
casting
Object-orientedconceptandhow
toimplementthem
Improvedpatternvisitor
Exceptionsandhowtouse
theminaninterpreter
Theimplicationofatype
Example:ADA
Alanguageissaidtobeweakly
typedwhenitallowscertinsnonexplicitcasting
Forinstance,fromintegerstofloatingpoints
53
54/54