Ruby objects

Question 1

All values are objects. T/F?

Answer 1

true

Question 2

What class do all Ruby objects inherit from?

Answer 2

Object

Question 3

What module does the object class mix in?

Answer 3

The Kernel module

Question 4

What does mixing in the Kernel module do to the built-in kernel functions?

Answer 4

it makes them globally accessible

Question 5

In Ruby, objects are directly manipulated. T/F?

Answer 5

False. References to objects are manipulated, not the objects themselves.

Question 6

Are method arguments pass by value or by reference?

Answer 6

by value

Question 7

What values are passed to methods?

Answer 7

object references

Question 8

Methods can use the object references to modify the underlying object. T/F?

Answer 8

true

Question 9

What types of values are Fixnum and Symbol treated as in a typical Ruby implementation?

Answer 9

immediate values

Question 10

What method is most often used to explicitly create an object?

Answer 10

new

Question 11

What does the following code do?

myObject = myClass.new

Answer 11

It creates a new object called myObject of type myClass.

Question 12

What class does the method new belong to?

Answer 12

Class

Question 13

What method method is invoked to initialize a new object?

Answer 13

initialize

Question 14

What are factory methods?

Answer 14

They are methods that allows you to initialize an object in different ways.

Question 15

What does the class method do?

Answer 15

It returns an object representing the class.

Example:
o = “test” # This is a value
o.class # Returns an object representing the String class

Question 16

What does the following code return?

a = 3.2
puts a.class.superclass

Answer 16

Numeric

Question 17

What class is the true root of the class hierarchy in Ruby 1.9?

Answer 17

BasicObject

Question 18

What method can be used to determine what class an object belongs to?

Answer 18

instance_of?

Question 19

What two methods are used to determine if an object is subclass of a class?

Answer 19

is_a?

kind_of?

Question 20

What operator can be used in place of the is_a? method?

Answer 20

===

Question 21

Define: object type

Answer 21

the set of behaviors that characterize the object or the set of methods it can respond to

Question 22

What method is used to determine if a method can be invoked on an object?

Answer 22

respond_to?

Question 23

What class enabled reading from and writing to string objects as if they were IO objects?

Answer 23

StringIO

Question 24

What does the equal? method test?

Answer 24

Whether two values refer to exactly the same object.

Question 25

What operator is used to allow distinct object instances to be tested for equality?

Answer 25

==

Question 26

How does the eql? method different from the == operator?

Answer 26

The eql? method does not type conversion on the operands.

Question 27

What is the case equality operator, ===, used for?

Answer 27

It tests whether the target value of a case statement matches any of the when clauses of that statement.

Question 28

What does the following expression return?

(1..10) === 5

Answer 28

true because 5 is in the range 1..10

Question 29

What does the following expression return?

/\d+/ === “123”

Answer 29

true because the string matches the regular expression

Question 30

What does the following expression return?

String === “s”

Answer 30

true because “s” is an instance of the class String

Question 31

What does the following expression return?

:s === “s”

Answer 31

true because the righthand operator is the same symbol as the left

Question 32

What does the following expression return?

“bug” <=> “string”

Answer 32

-1 because “bug” is less than “string” (the letter “b” comes before the letter “s” in the alphabet)

Question 33

What does the following expression return?

1.between?(0,10)

Answer 33

true because 0 <= 1 <= 10

Question 34

What mixin defines the between? method?

Answer 34

Comparable

Question 35

What mixin defines equality operators in terms of <=>?

Answer 35

Comparable

Question 36

What method is used to return a String representation of an object?

Answer 36

to_s

Question 37

What method is used to return an Integer representation of an object?

Answer 37

to_i

Question 38

What method is used to return an Float representation of an object?

Answer 38

to_f

Question 39

What method is used to return an Array representation of an object?

Answer 39

of_a

Question 40

What method is an alternative to the to_s method and is useful for debugging?

Answer 40

to_s

Question 41

What are the two methods used for copying objects?

Answer 41

clone and dup

Question 42

What method can be used to create a deep copy of an object?

Answer 42

initialize_copy

Question 43

The clone method copies the frozen state while dup does not. T/F?

Answer 43

true

Question 44

the clone method copies and singleton methods of the object while dup does not. T/F?

Answer 44

true

Question 45

What does the Marshal.dump class method do?

Answer 45

It saves the state of the object.

Question 46

What method can be used to mark an object as untrusted user input?

Answer 46

taint

Question 47

What method can be used to test if an object is tainted?

Answer 47

tainted?

Question 48

What method is used to unmark an object as tainted?

Answer 48

untaint