Object Oriented Languages

Question 1

Purpose of OOLs

Answer 1

Current languages could not simulate real world entities properly, better cohesion and coupling.

Question 2

OOL Influences

Answer 2

Procedural Languages, Lambda Calculus, Types

Question 3

class hierarchy

Answer 3

expresses relationship between classes

Question 4

polymorphism

Answer 4

function is applicable to more than one type

Question 5

white box inheritance

Answer 5

sharing, but breaks encapsulation. Inherited class internals visible to subclass

Question 6

inheritance

Answer 6

reusing the definition of one type of object to define another type of object

Question 7

encapsulation

Answer 7

bundles slots and the methods that operate on those slots into a single unit, leads to loose coupling and strong cohesion

Question 8

black box inheritance

Answer 8

uses functionality of superclass without exposing the superclasses’ implementation details, doesn’t break encapsulation

Question 9

cohesion

Answer 9

how much code belongs together

Question 10

weak cohesion

Answer 10

coincidental bundling, similar functions

Question 11

medium cohesion

Answer 11

components provide similar services or functions

Question 12

strong cohesion

Answer 12

each component contributes to software function

Question 13

coupling

Answer 13

how connected the code is

Question 14

loose coupling

Answer 14

changes in A are unlikely to affect B

Question 15

tight coupling

Answer 15

changes in A are likely to affect B, puts change costs up

Question 16

best type of coupling

Answer 16

loose

Question 17

best type of cohesion

Answer 17

strong

Question 18

strong cohesion and loose coupling

Answer 18

results in understandability, maintainability and adaptability

Question 19

generic functions

Answer 19

a function that can run on multiple data types

fn <T>my_func(p: T) {} in rust, same as a polymorphic function

Question 20

generic functions features

Answer 20

classes, instances, methods, multi methods, slots, singe/multiple inheritance

Question 21

prototyping

Answer 21

simplest kind of OO, object = attributes + behaviours

Question 22

delegation

Answer 22

enables the sharing of behaviour, object = attributes + behaviours + parent

Question 23

traits

Answer 23

sharing behaviour (methods)

Question 24

maps

Answer 24

sharing structure (slots)

Question 25

class

Answer 25

shares behaviour(methods) and structure(slots), object stored data and link to class

Question 26

method dispatch

Answer 26

selecting which method implementaiton to use at runtime

Question 27

single dispatch

Answer 27

search up the inheritance chain until method matching message is found

Question 28

multiple dispatch

Answer 28

for some operations method selection depends on more than one item of information ## Footnote MI is classes having multiple parents, while multiple dispatch is choosing a method using multiple arguments

Question 29

class precedence list

Answer 29

the linearised list of the superclasses of a class, defining the order of inheritance

Question 30

single inheritance in CPL

Answer 30

a list of classes in proximity order, nearest first, between a class and the root of the hierarchy

Question 31

multiple inheritance in CPL

Answer 31

same as SI expect for special rules are needed to handle duplications arising from join in the class hierarchy

Question 32

method composition

Answer 32

methods in a class combine methods from composed classes

Question 33

visual single inheritance

Answer 33

tree

Question 34

visual multiple inheritance

Answer 34

directed acyclic graph

Question 35

multiple inheritance benefits

Answer 35

* possibly better sharing and reuse of code * better fit with situation being modelled

Question 36

an ontology

Answer 36

* reflects structure of the world * addressed concept relationships * physical representation is not relevant

Question 37

an oo class structure

Answer 37

* relects structure of data and code * is usually about behaviour (methods) * physical representation is crucial

Question 38

MI downsides

Answer 38

* hard to use a complex MI in practice * prededence list computation can be unpredicatable * more fragile with respect to changes (tight coupling)

Question 39

single inheritance with single dispatch

Answer 39

if the class of the current object has a method defined, use it; else recurse to the parent class

Question 40

linearisation

Answer 40

flattening a class hierarchy to make a CPL, many languages have a builtin linearisatoin algorithm

Question 41

monotonic CPL

Answer 41

the CPL of a class is consistent with the CPL of its parents

Question 42

C3 linearisation

Answer 42

* used by many languages * fairly easy to implement * its monotonic * used in python, perl, etc

Question 43

dynamic lookup

Answer 43

when a message is sent to an object, the method to be executed is determined by the way that the object is implemented | the object “chooses” how to respond to a message, and different objects

Question 44

abstraction

Answer 44

implementation details are hidden inside a program unit with a specific interface

Question 45

subtyping

Answer 45

means that if some object a has all of the functionality of another object b, then we may use a in any context expecting b

Question 46

C++ Multiple Inheritance

Answer 46

* everything is defined by the programmer * programmer controls base class replication through virtual inheritance * explicitly denote origin of inherited members

Question 47

C++ Virtual Inheritance

Answer 47

in the case that a subclass is set to inherit two copies of a base class virtual inheritance ensures that only a single copy is inherited

Question 48

Class Composition

Answer 48

alternative to MI, composed classes are variables in the object composing Istream and Ostream we write class IOStream: public: Istream i; Ostream o; method and slot lookup is done at coding time by the programmer (str.o.ptr or str.i.ptr)

Question 49

Liskov Substitution

Answer 49

Suppose S is a subtype of T. Then whenever we need an instance of type T we can use an instance of type S, and our code should still operate correctly. | a subclass must honor the behavioural contract of its superclass

Question 50

reflection

Answer 50

the transformation and insertion of data from the application into the processor of the application | a language can inspect and alter itself ## Footnote self-modifying programs are dangerous and hard to understand or control

Question 51

metaobject programming

Answer 51

provides reflection through a framework which makes it safe to use

Question 52

reification

Answer 52

the extraction and presentation of data from the processor of an application to the application | allows a program to examine its own structure of behaviour ## Footnote * debuggers reify and reflect * Java's class-loader reflects * eval in Lisp reflects