introduction to ruby

Question 1

History of ruby:
What was ruby influenced by?

Answer 1

•It was also influenced by Eiffel and Lisp, Perl with Smalltalk-like features.

Question 2

What is Ruby?​

Answer 2

Ruby is a dynamic, reflective, general-purpose object-oriented programming language.

Question 3

Ruby and Java Comparison

Answer 3

•Ruby

sleep 100

•Java

public class sleep{

public static void main (String[] args) throws InterruptedException {

Thread.sleep (100*1000);
}
}

Question 4

Who was the designer of Ruby?

Answer 4

Ruby was first designed and developed in the mid-1990s by Yukihiro “Matz” Matsumoto in Japan.”

Question 5

The ruby language syntax is sensitive to the…

Answer 5

capitalization of identifiers, in all cases treating capitalized variables as constants.

Question 6

•The sigils $ and @ do not indicate variable data type as in Perl, but rather….

Answer 6

function as scope resolution operators.

Question 7

•One of ruby’s features is that it is thoroughly object-oriented with _____ , ______ , _______

Answer 7

inheritance mixins and metaclasses

Question 8

What is Duck typing?

Answer 8

you don’t need a type in order to invoke an existing method on an object - if a method is defined on it, you can invoke it.

The name comes from the phrase “If it looks like a duck and quacks like a duck, it’s a duck”

Question 9

What is Dynamic typing?

Answer 9

Dynamic typing just says that types are associated with run-time values, not with static variables and parameters.

Question 10

Everything is an _________ (even statements) and everything is executed imperatively (even _________)

Answer 10

•Everything is an expression (even statements) and everything is executed imperatively (even declarations)

Question 11

A ruby feature is that Succinct and flexible _____ that minimizes ______________ and serves as a foundation for _______________ languages.

Answer 11

Succinct and flexible syntax that minimizes syntactic noise and serves as a foundation for domain-specific languages

Question 12

Ruby features: Dynamic _________ and ________ of objects to facilitate ______________

Answer 12

Dynamic reflection and alteration of objects to facilitate metaprogramming

Question 13

Ruby features: ___________, _________ and _________, with a unique block syntax

Answer 13

•Lexical closures, iterators and generators, with a unique block syntax

Question 14

Ruby feature: Literal notation for ______, ______, ________________ and _______

Answer 14

Literal notation for arrays, hashes, regular expressions and symbols

Question 15

Ruby feature: •Embedding code in _______(interpolation)

Answer 15

Ruby feature: •Embedding code in strings (interpolation)

Question 16

Ruby features: _______arguments

Answer 16

Default arguments

Question 17

Ruby features: •________ collection

Answer 17

•Garbage collection

Question 18

Ruby features: •Four levels of variable scope (_____, ______, __________, and ______) denoted by sigils or the lack thereof

Answer 18

•Four levels of variable scope (global, class, instance, and local) denoted by sigils or the lack thereof

Question 19

Ruby features: Strict ________ rules (everything is _____except ____and ___)

Answer 19

Strict boolean coercion rules (everything is true except false and nil)

Question 20

Ruby features: __________ continuations

Answer 20

First-class continuations

Question 21

Ruby features: ________ handling

Answer 21

•Exception handling

Question 22

Ruby features: ________ overloading

Answer 22

Operator overloading

Question 23

Ruby features: Built-in support for ________numbers, ________ numbers and ________ arithmetic

Answer 23

Built-in support for rational numbers, complex numbers and arbitrary-precision arithmetic

Question 24

Ruby features: Custom dispatch behavior (through : ________and : ________)

Answer 24

Ruby features: Custom dispatch behavior (through method_missing and const_missing)

Question 25

Ruby features: Native ________ and cooperative ________ (________are 1.9/YARV feature)

Answer 25

•Native threads and cooperative fibers (fibers are 1.9/YARV feature)

Question 26

Ruby features: Initial support for ________ and multiple character ________ (no ICU support)

Answer 26

•Initial support for Unicode and multiple character encodings (no ICU support)

Question 27

Ruby features: ________on all major platforms

Answer 27

•Implemented on all major platforms

Question 28

Ruby features:Native plug-in ____in __

Answer 28

•Native plug-in API in C

Question 29

Ruby features:Large standard ________

Answer 29

•Large standard library

Question 30

Ruby deviations:_________ evaluation of non-boolean data is strict: 0, “” and [] are all evaluated to true.

Answer 30

Boolean evaluation of non-boolean data is strict: 0, “” and [] are all evaluated to true.

–Only false and nil are FALSE

Question 31

Ruby deviations: To denote a _________ without a decimal component, one must follow with a ________ (99.0) or an explicit conversion (____). It is ________ to append a dot (99.) since numbers are susceptible to _____ _____.

Answer 31

•To denote a floating point without a decimal component, one must follow with a zero digit (99.0) or an explicit conversion (99.to_f). It is insufficient to append a dot (99.) since numbers are susceptible to method syntax.

Question 32

Variables always hold _________ to objects.

Answer 32

Variables always hold references to objects.

Question 33

Ruby is object-oriented: every value is an ______, including classes and ________ of types that many other languages designate as ______ (such as integers, booleans, and “null”).

Answer 33

•Ruby is object-oriented: every value is an object, including classes and instances of types that many other languages designate as primitives (such as integers, booleans, and “null”).

Question 34

Every function is a _____ and ______ are always called on an ______.

Answer 34

•Every function is a method and methods are always called on an object.

Question 35

Ruby features: Centralized package management through ________

Answer 35

•Centralized package management through RubyGems

Question 36

What are expressions in ruby?

Answer 36

•Expressions are Objects and return values

Question 37

Methods defined at the top level _____ become members of the _____ class. Since this class is an ancestor of every other class, such methods can be called on any object.

Answer 37

•Methods defined at the top level scope become members of the Object class. Since this class is an ancestor of every other class, such methods can be called on any object.

Question 38

Ruby outputs: All _______ also have an “inspect” method

–Includes list of _____ variables

Answer 38

•All Object’s also have an “inspect” method

–Includes list of instance variables

Question 39

Ruby outputs: All Object’s have a “to_s” ______

And you probably want to define one for your _____

Answer 39

•All Object’s have a “to_s” method

–And you probably want to define one for your objects

Question 40

Ruby methods: Has a “______” statement

Answer 40

Has a “return” statement

Question 41

Ruby methods: Take ________

Answer 41

Take arguments

Question 42

Ruby methods: Between “___” “___” pairs

Answer 42

•Between “def” “end” pairs

Question 43

Ruby methods: But also returns last _________ ________

Answer 43

But also returns last expression evaluated

Question 44

Creating and Extending Objects in Ruby

Answer 44

obj = Object.new

def obj.talk

puts “I am an object”

end

obj.talk

Question 45

Objects have Identifiers

Answer 45

s1 = “Hello”

s2 = “Hello”

p s1.object_id

p s2.object_id

Question 46

What does this output?

s1 = “Hello”

s2 = “Hello”

p s1.object_id

p s2.object_id

Answer 46

$ ruby ref.rb

70235101628760

70235101628740

Question 47

Passing Parameters

Answer 47

obj = Object.new

def obj.c2f(c)

c * 9.0 / 5 + 32

end

p obj.c2f(100)

p obj.c2f 100

Question 48

What does this output?

obj = Object.new

def obj.c2f(c)

c * 9.0 / 5 + 32

end

p obj.c2f(100)

p obj.c2f 100

Answer 48

$ ruby ref.rb

212. 0
213. 0

Question 49

Optional Arguments

Answer 49

obj = Object.new

def obj.multi(*x)

p x

end

obj. multi()
obj. multi(1)
obj. multi(1,2,3)

Question 50

What does this output?

obj = Object.new

def obj.multi(*x)

p x

end

obj. multi()
obj. multi(1)
obj. multi(1,2,3)

Answer 50

$ ruby ref.rb

[]

[1]

[1, 2, 3]

Question 51

Ending Optional Arguments

Answer 51

obj = Object.new

def obj.optional(a,b,*c)

p a,b,c

end

obj. optional(1, 2)
obj. optional(1, 2, 3)
obj. optional(1, 2, 3, 4)

Question 52

What does this code output?

obj = Object.new

def obj.optional(a,b,*c)

p a,b,c

end

obj. optional(1, 2)
obj. optional(1, 2, 3)
obj. optional(1, 2, 3, 4)

Answer 52

$ ruby ref.rb

1

2

[]

1

2

[3]

1

2

[3, 4]

Question 53

Default Arguments

Answer 53

obj = Object.new

def obj.default(a,b=3)

p “#{a}, #{b}”

end

obj. default(1)
obj. default(1,4)

Question 54

What is the output of this code?

obj = Object.new

def obj.default(a,b=3)

p “#{a}, #{b}”

end

obj. default(1)
obj. default(1,4)

Answer 54

$ ruby ref.rb

“1, 3”

“1, 4”

Question 55

List Ruby variables

Answer 55

• Locals: start with lowercase or underscore
• Instance: start with ‘@’
• Class: start with ‘@@’
• Globals: start with ‘$’
• Constants begin with uppercase

Question 56

Local Variables

Answer 56

•Locals: start with lowercase or underscore

Question 57

Instance Variables

Answer 57

•Instance: start with ‘@’

Question 58

Class Variables

Answer 58

•Class: start with ‘@@’

Question 59

Global Variables

Answer 59

•Globals: start with ‘$’

Question 60

Constant Variables

Answer 60

•Constants begin with uppercase

Question 61

All Variables are References

Answer 61

•All Variables are References

–No base types as in other language (e.g. integer, float, string, etc.)

•Refer to Objects

Question 62

All Variables are References

a = “Hello”

b = a

p a

p b

b = “Goodbye”

p a

p b

What does this output?

Answer 62

$ ruby ref.rb

“Hello”

“Hello”

“Hello”

“Goodbye”

Question 63

Aliases

a = “Hello”

b = a

p a

p b

a.replace(“Yo”)

p a

p b

What does this output?

Answer 63

$ ruby ref.rb

“Hello”

“Hello”

“Yo”

“Yo”

Question 64

Freeze Method

a = “Hello”

a. freeze
a. replace(“Yo”)

What will happen when we run this code?

Answer 64

$ ruby ref.rb

ref.rb:3:in `replace’: can’t modify frozen String (RuntimeError)

from ref.rb:3:in `<main>’</main>

Question 65

Ruby Classes

Answer 65

• Class names are constants
• Define methods/messages
• Can reopen
• Can override

Question 66

Override

class A

def m

“one”

end

def m

“two”

end

end

p A.new.m

What will this happen?

Answer 66

$ ruby ref.rb

“two”

Question 67

Reopen

class A

def m

“one”

end

def m

“two”

end

end

p A.new.n

What will this code output?

Answer 67

$ ruby ref.rb

ref.rb:10:in <main>': undefined method n’ for #<0x007f89f411cfd0> (NoMethodError)0x007f89f411cfd0></main>

Question 68

Reopen

What will this code output?

Answer 68

$ ruby ref.rb

“two”

“three”

Question 69

Initializers and Accessors

class B

def initialize(a, b)

@one = a

@two = b

end

def one

@one

end

def two

@two

end

end

b = B.new(1, 2)

p b.one

p b.two

What will this code output?

Answer 69

$ ruby ref.rb

1

2

Question 70

Attribute Reader

class C

attr_reader :one, :two

def initialize(a,b)

@one = a

@two = b

end

end

c = C.new(3,4)

p c.one

p c.two

What will this output?

Answer 70

$ ruby ref.rb

3

4

Question 71

Writing and Both methods

Answer 71

•attr_writer and attr_accessor

Question 72

Ruby inheritance

Answer 72

•Single

–Like Java, unlike C++

•Receives all functionality from base (parent) class

–Can call base class function of the same name by “super”

• Adds specificity
• Modules

–“Mix ins”

Question 73

Inheritance Code

Answer 73

class Human

attr_reader :personality, :income

def initialize(p, i)

@personality = p

@income = i

end

end

class Programmer < Human

def initialize(p, i)

super(p-100, i+100)

end

end

Question 74

Superclasses

Answer 74

>> Programmer.superclass

=> Human

>> Programmer.superclass.superclass

=> Object

Question 75

Class Variables and Methods

Answer 75

• Variables or methods where only one exists per class
• Every object of the class shares them

Question 76

Class Variable

class Number

@@count = 0

def initialize(val)

@val = val

@@count = @@count + 1

end

def Number.count

@@count

end

end

a = Number.new(1)

b = Number.new(11)

c = Number.new(111)

p Number.count

What will this output?

Answer 76

$ ruby ref.rb

3

Question 77

“Constant”

Z = 1

p Z

Z = 2

p Z

What will this output?

Answer 77

$ ruby ref.rb

1

ref. rb:3: warning: already initialized constant Z
ref. rb:1: warning: previous definition of Z was here

2

Question 78

3 Ruby Constants concepts

Answer 78

• Constants defined within a class or module may be accessed anywhere within the class or module.
• Outside the class or module, they may be accessed using the scope operator, :: prefixed by an expression that returns the appropriate class or module.
• Constants defined outside any class or module may be accessed as it is or by using the scope operator with no prefix.

Question 79

2 Ruby constants

Answer 79

• Constants may not be defined in methods.
• Constants may be added to existing classes and modules from the outside by using the class or module name and the scope operator before the constant name.

Question 80

Class Methods

What will this output?

Answer 80

<0x007ffb3c84c940>0x007ffb3c84c940>

$ ruby ref.rb

main

C

C

Question 81

Scope

class A p A::X

X=1 p A::B::X

class B p A::B::C::X

X=2

class C

X=3

end

end

end

What will this output?

Answer 81

$ ruby ref.rb

1

2

3

Question 82

Inherited Class Variables

What will this output?

class Parent

@@age = 40

def age

@@age

end

end

class Child < Parent

@@age = 10

end

p Parent.new.age

Answer 82

$ ruby ref.rb

10

Question 83

Private and Protected

What will this output?

Answer 83

$ ruby ref.rb

“yep”

“derived”

ref.rb:25:in <main>': private method nope’ called for #<0x007fb869994408> (NoMethodError)0x007fb869994408></main>

Question 84

Conditionals

Answer 84

• if/else/elsif/end
• if not (x ==1)
• if !(x==1)
• unless x==1/else/end
• puts x if x>0
• puts x unless x == 0

Question 85

Allocation in Conditionals

if false

x = 1

end

p x

p y

What will this output?

Answer 85

$ ruby ref.rb

nil

ref.rb:5:in <main>': undefined local variable or method y’ for main:Object (NameError)</main>

Question 86

Assignment in Conditionals

if x = 1

p “Hi”

end

What will this output?

Answer 86

$ ruby ref.rb

ref.rb:1: warning: found = in conditional, should be ==

“Hi”

Question 87

Operator Override

class Person

attr_reader :name, :age

def initialize(name,age)

@name = name

@age = age

end

def ==(other)

self.age == other.age

end

end

person1 = Person.new(“Alice”, 50)

person2 = Person.new(“Bob”, 50)

person3 = Person.new(“Alice”, 40)

p person1 == person2

p person1 == person3

What will this output?

Answer 87

$ ruby ref.rb

true

false

Question 88

Case

a = “This”

case a

when “That”

p “I’m a that”

when “This”

p “I’m a this”

else

p “I’m neither”

end

What will this output?

Answer 88

$ ruby ref.rb

“I’m a this”

Question 89

Override When’s “===“

class Person

attr_reader :name, :age

def initialize(name,age)

@name = name

@age = age

end

def ===(other)

self.age == other.age

end

end

person1 = Person.new(“Alice”, 50)

person2 = Person.new(“Bob”, 50)

def Person.compare(p1, p2)

print “#{p1.name} and #{p2.name}”

case p1

when p2

print “ are “

else

print “ aren’t “

end

print “the same\n”

end

Person.compare(person1, person2)

Person.compare(person1, person3)

What will this output?

Answer 89

$ ruby equal.rb

Alice and Bob are the same

Alice and Alice aren’t the same

Question 90

Else in Case

5.times do |i|

case i

when 1

p “one”

when 2

p “two”

else

p i

end

end

What will this output?

Answer 90

0

“one”

“two”

3

4

Question 91

Loops

n = 0

loop do

n = n + 1

puts n

break if n > 5

end

What will this output?

Answer 91

1

2

3

4

5

6

Question 92

While

n = 0

while n < 5

n = n + 1

puts n

end

What will this output?

Answer 92

1

2

3

4

5

Question 93

Begin/While

n = 0

begin

n = n + 1

puts n

end while n < 5

What will this output?

Answer 93

1

2

3

4

5

Question 94

Until

n = 0

until n > 5

n = n + 1

puts n

end

What will this output?

Answer 94

1

2

3

4

5

6

Question 95

Iterating on Lists

c=[“one”, “two”, “three”, “four”, “five”]

for i in c

puts i

end

What will this output?

Answer 95

$ ruby ref.rb

one

two

three

four

five

Question 96

3 loop features

Answer 96

• Loops really just repeatedly execute code blocks
• I.e.: they are iterators
• Iterators repeatedly “yield” to code blocks

Question 97

Code Blocks

Answer 97

• Defined inside “{}”or “do”
• Passed as parameters
• Called via “yield”

Question 98

Blocks and Iterators

curlies when something is returned

puts [1,2,3].map {|n| n*10}

do when nothing is returned

[1,2,3].map do |n|

puts n*10

end

What will this output?

Answer 98

$ ruby ref.rb

10

20

30

10

20

30

Question 99

my_times method

class Integer

def my_times

c = 0

while c < self

yield c

c += 1

end

self

end

end

a = 0.my_times {|i| p i}

puts “a = #{a}”

a = 5.my_times {|i| p i}

puts “a = #{a}”

a = -5.my_times {|i| p i}

puts “a = #{a}”

What will this output?

Answer 99

$ ruby ref.rb

a = 0

0

1

2

3

4

a = 5

a = -5

Question 100

Exceptions

begin

a = 1 / 0

rescue ZeroDivisionError => e

puts e.message

puts e.backtrace

end

What will this output?

Answer 100

$ ruby ref.rb

divided by 0

ref. rb:2:in /' ref. rb:2:in <main>’</main>

Question 101

Ruby Symbols

Answer 101

• Begin with ‘:’
• More similar to integers than strings
• Are immutable
• Are unique
• Used to refer to methods
• Often used in hashes

Question 102

Symbol Example

p “abc”.object_id

p “abc”.object_id

p :abc.object_id

p :abc.object_id

What will this output?

Answer 102

$ ruby ref.rb

70190050355780

70190050355680

407688

407688

Question 103

Numbers

Answer 103

•Numeric

–Float

–Integer

• Fixnum
• Bignum

Question 104

Hashes

Answer 104

• Key/value pairs
• Use “{}” as literal

Question 105

Hashing

hash = {

“red” => “ruby”,

“white” => “diamond”,

“green” => “emerald”

}

hash.each_with_index do

|(key,value),i|

puts “#{i} is #{key} => #{value}”

end

What will this output?

Answer 105

$ ruby ref.rb

0 is red => ruby

1 is white => diamond

2 is green => emerald

Question 106

Older Symbol

Answer 106

hash = {

:red => “ruby”,

:white => “diamond”,

:green => “emerald”

}

Question 107

Newer Symbol

Answer 107

hash = {

red: “ruby”,
white: “diamond”,
green: “emerald”

}

Question 108

Array Initialization

Answer 108

>> Array.new(3)

=> [nil, nil, nil]

>> Array.new(3, “Hi”)

=> [“Hi”, “Hi”, “Hi”]

>> n = 0

=> 0

>> Array.new(3){n+=1; n*10}

=> [10, 20, 30]

Question 109

More Array Initialization​

Answer 109

>> a = Array.new(3, “Hi”)

=> [“Hi”, “Hi”, “Hi”]

>> a[0].object_id

=> 2189467100

>> a[1].object_id

=> 2189467100

>> a[2].object_id

=> 2189467100

>> a[0].replace(“Bye”)

=> “Bye”

>> a

=> [“Bye”, “Bye”, “Bye”]

Question 110

Array Methods

a = [1, 2, [3, 4], [[5, 6], [7, 8]]]

p a.flatten

p a.reverse

p [1, 2, 3, 3, 3, 4, 1].uniq

p [“2”, 1, 5, “3”, 4, “6”].sort_by {|a| a.to_i}

What will this output?

Answer 110

$ ruby ref.rb

[1, 2, 3, 4, 5, 6, 7, 8]

[[[5, 6], [7, 8]], [3, 4], 2, 1]

[1, 2, 3, 4]

[1, “2”, “3”, 4, 5, “6”]

Question 111

Ranges

p (1..5).include?(5)

p (1…5).include?(5)

r = 1..10

p r.one? {|n| n == 5}

p r.any? {|n| n > 5}

p r.count {|n| n > 5}

p r.find_all {|n| n > 5}

What will this out?

Answer 111

$ ruby ref.rb

true

false

true

true

5

[6, 7, 8, 9, 10]

Question 112

Global Regular Expression Print

misc=[75, “hello”, 10…20, “goodbye”]

p misc.grep(String)

p misc.grep(/o/)

p misc.grep(50..100)

p misc.grep(Fixnum)

p misc.grep(Integer)

What will this output?

Answer 112

$ ruby ref.rb

[“hello”, “goodbye”]

[“hello”, “goodbye”]

[75]

[75]

[75]

Question 113

Each Takes an Array and a Block

[1,2,3].each {|i| puts “Received #{i}”}

Answer 113

$ ruby ref.rb

Received 1

Received 2

Received 3

Question 114

Map

Answer 114

•Takes an array and returns an array

>> numbers = [“one”, “two”, “three”, “four”, “five”]

=> [“one”, “two”, “three”, “four”, “five”]

>> numbers.map {|number| number.capitalize}

=> [“One”, “Two”, “Three”, “Four”, “Five”]

Question 115

Proc’s

Answer 115

• Ruby has first-class code blocks called “Proc”s
• Are a combination of code and context
• Proc’s can be assigned to variables, be array elements, etc., etc.
• Can be used for closures

Question 116

Closure

def multiply_by(m)

Proc.new {|x| x * m}

end

p10 = multiply_by 10

p12 = multiply_by 12

p p10.call(10)

p p10.call(11)

p p12.call(1)

p p12.call(6)
What does this output?

Answer 116

$ ruby ref.rb

100

110

12

72

Question 118

Another Closure

def make_counter

n = 0

Proc.new { n += 1 }

end

c1 = make_counter

c2 = make_counter

p c1.call

p c1.call

p c1.call

p c2.call

p c1.call

p c2.call

What does this ooutput?

Answer 118

$ ruby ref.rb

1

2

3

1

4

2

Question 119

Ruby features: Interactive ________(a REPL (________/________/________)) – IRB

Answer 119

•Interactive Ruby Shell (a REPL (Read/Execute/Print Loop)) – IRB