Intro to ruby

Intro to Ruby
Women Who Code Belfast

h.campbell@kainos.com : hcampbell07 : heatherjcampbell.com

Syntactic

Sugar

Productive
Developers

• Everything is an Expression

• Everything is an Object
• Supports Dynamic Reflection

current_count = 5
final_salary = 30000.00

Snake Case
Readable

String.methods.sort
String.instance_methods.sort

Methods

my_array.empty?
person.retired?

True or False

str.upcase vs str.upcase!

Create New vs
Modify Existing

io.rb
print “Enter your name: ”
name = gets
puts name.strip + “ is learning Ruby”

Input / Output

[4,2,3,5].sort.map{ |e| e * e}.join(',')
# "4,9,16,25"

Method Chaining

• Write some code to ask a user to input a
number. Take the number multiply it by
10 and display it back to the user
• Find a method to capitalize a string
• Check the class of 1. (using the .class
method) then find a method to check if
the number is even

Exercises

true.class
# TrueClass
false.class
# FalseClass
true.to_s
# "true"

Boolean

1.class
# Fixnum

1111111111.class
# Bignum

Fixnum.superclass
# Integer

Bignum.superclass
# Integer

111_000_000.class
# Fixnum

1.2345.class
# Float

Numbers

String.method.count
# Lots of helpful methods!
"Ruby" * 4
# "RubyRubyRubyRuby"
"Ruby" + " " + "Ruby"
# "Ruby Ruby"
a = "I don’t know Ruby"
a*"don’t"+ = "do"
# "I do know Ruby"

String

number_of_girls = 4
number_of_boys = 6
puts "number of girls #{number_of_girls}"
puts "number of boys #{number_of_boys}"
puts "number of people
#{number_of_boys + number_of_girls}"

Interpolation

phone = "(028 90)454 545"
phone.gsub!(/D/, "")
puts "Phone Number : #{phone}"
# "02890454545"

puts "Heather Campbell".gsub(/([a-zA-Z]+)
([a-zA-Z]+)/, "2, 1")
# "Campbell, Heather"

Regex

attr_accessor :driver
:small :medium :large
a = :small
b = :small
a.object_id == b.object_id
# true
:small.to_s
# "small "

"small".to_sym
# :small

Symbols

arr = [1,2,'three', :big]
arr.size # 4
arr.empty? # false
arr[1] # 2
arr[-1] # :big
arr[1..3] # [2,'three', :big]
arr[4..5] = [:east, :west]
# [1,2,'three', :big, :east, :west]
arr << 10
# [1,2,'three', :big, :east, :west,10]

Arrays

[1,2,3].map { |e| e * e}
# [1,4,9]
[2,2,3].reduce{|total,v| total * v}
# 12
['act', 'bat', 'them'] .all? { |w| w.length >= 3 }
# true

Enumerable

h = {'France' => 'Paris', 'Ireland' => 'Dublin' }
h = {France: 'Paris', Ireland: 'Dublin' }
h[:France]
# 'Paris‘
h[:Italy] = 'Rome'
# h = {France: 'Paris', Ireland: 'Dublin', Italy:
# 'Rome' }
h.each {|k,v| puts "key: #{k} t value: #{v}"}
h.any? { |k,v| v == 'Rome' }

Hashes

(1..5).each{|v| p v}
# 1,2,3,4,5
(1…5).each{|v| p v}
# 1,2,3,4
(10..20).include?(19) # true
(2..5).end # 5
("aa".."ae").each{|v| p v}
# "aa","ab","ac","ad","ae"

Ranges

def get_values; [1,2,3,4]; end;
first, _, _, last = get_values
# first = 1, last = 4
a, *b, c = get_values
# a = 1, b = [2,3],c = 4
r = (0..5)
a = [1,2,*r]
# a = [1,2,0,1,2,3,4,5]

Splat Operator

•
•

Separate an array [1,2,3,4] into 2 variables
one holding the head of the array (i.e 1) and
the other the rest of the array [2,3,4]
Create a hash of months and days in a month
e.g. {January: 31, ..}. For each month print out
the month name and number of days. Then
print out totals days in year by summing the
hashes values

Exercises

if mark > 75
report = "great"
elsif mark > 50
report = "good"
else
report = "needs work"
end

report =
if mark > 75 then
"great"
elsif mark > 50 then
"good"
else
"needs work"
end

if else

if !order.nil?
order.calculate_tax
end
order.calculate_tax unless order.nil?

unless

speed = 60
limit = 40
speed > limit ? puts("Speeding!") : puts("Within
Limit")

ternary operator

mark = 42 && mark * 2
# translates to mark = (42 && mark) * 2
mark = 42 and mark * 2
# returns 84
post = Posts.locate(post_id) and post.publish
# publishes post if it is located
if engine.cut_out?
engine.restart or enable_emergency_power
end

and / or

grade = case mark
when 90..100
"A"
when 70..89
"B"
when 60..69
"C"
when 50..59
"D"
when 40..49
"E"
else
"F"
end

case unit
when String
puts "A String!"
when TrueClass
puts "So True!"
when FalseClass
puts "So False!"
end

case

while count < max
puts "Inside the loop. count = #{count}"
count +=1
end
puts "count = #{count += 1}" while count < max

while

until count > max
count +=1
end
array = [1,2,3,4,5,6,7]
array.pop until array.length < 3

until

begin
count +=1
end while count < max

looping block

for count in (1..10)
puts "Inside the loop: count = #{count}"
end

for

animals = {cat: "meow ", cow: "moo "}

animals.each do |k,v|
puts "The #{k} goes #{v}"
end
animals = {cat: "meow ", cow: "moo "}

animals.each {|k,v| puts "The #{k} goes #{v} "}

iterators

magic_number = 5; found = false; i = 0; input = 0;
while i < 3
print "Please enter a number between 1 and 10: "
input = gets.to_i
unless input.between?(1,10)
print "invalid number"; redo
end
if input == magic_number
found = true; break
end
i += 1
end
found ? put "found! " : put " bad luck "

flow control

def display_content(name)
f = File.open(name, 'r')
line_num=0
# raise 'A test exception.'
f.each {|line| print "#{line_num += 1} #{line}"}
rescue Exception => e
puts "ooops"; puts e.message; puts e.backtrace
else
puts "nSuccessfully displayed!"
ensure
if f then f.close; puts "file safely closed"; end
end

exception handling

def get_patients()
patients = API.request("/patients")
rescue RuntimeError => e
attempts ||= 0
attempts += 1
if attempts < 3
puts e.message + ". Retrying request. “
retry
else
puts "Failed to retrieve patients"
raise
end
end

exception handling

•
•
•
•

Write some conditional logic to capitalize a
string if it is not in uppercase
Print out your name 10 times
Print the string “This is sentence number 1”
where the number 1 changes from 1 to 10
Write a case statements which outputs
“Integer” if the variable is an integer, “Float” if
it is a floating point number or else “don’t
know!”

Exercises

class Vehicle
def drive(destination)
@destination = destination
end

end

Classes

class Vehicle
attr_accessor :destination

self.destination = destination
# do more drive stuff
end
end

Accessors

attr_accessor
attr_reader
attr_writer

Accessors

class Vehicle
attr_accessor :colour, :make
def initialize(colour, make)
@make = make
@colour = colour
end
end

Constructor

class SuperCar < Vehicle
puts 'driving super fast'
end
end

Inheritance

attr_accessor :driver

def drive(circuit, driver)
self.driver = driver
puts 'driving super fast'
end
end

Inheritance

“If it walks like a duck and talks
like a duck, it must be a duck”

Duck Typing

class Person
def quack()
puts 'pretends to quack'
end
end
class Duck
def quack()
puts 'quack quack'
end
end

Duck Typing

def call_quack(duck)
duck.quack
end
call_quack(Duck.new)
# quack quack

call_quack(Person.new)
# pretends to quack

Duck Typing

class Vehicle

class Vehicle

def crash()
explode
end

def crash()
explode
end

private
def explode()
puts "Boom!"
end
end

def explode()
puts "Boom!"
end
private :explode
end

Method Visibility

def explode()
puts "Massive Boom!"
end
end

Method Visibility

result = class Test
answer = 7+5
puts " Calculating in class: " + answer.to_s
answer
end
puts "Output of the class: " + result.to_s

Executable

class Rocket
….

end

r = Rocket.new
class Rocket
def land()
puts "Back on Earth"
end
end

r.land

Open Classes

class String
def shout
self.upcase!
self + "!!!"
end
def empty?
true
end
end

Monkey Patching

a = "abc"
b=a
c = "abc"
a.equal?(b)
# true
a.equal?(c)
# false
a == b
# true
a == c
# true

Equality

•
•
•
•
•
•

Create a class to represent a Computer
Create an instance of the Computer called
computer
Add a starting_up method
Create a class WindowsComputer which
inherits from Computer
Create an instance of the WindowsComputer
called wcomputer and call starting_up on it
Alter WindowsComputer to allow the user to
set a name value when they create an
instance. Allow the user to set and get the
name attribute

Exercises

# Java
public Car() , …public Car(String make) { }
public Car(String make, String model) { }
public Car(String make, String model, String colour) { }
# Ruby
def initialize (make = :Ford,
model = Car.get_default_model(make),
colour = (make == :Ferrari ? 'red' : 'silver') )
…
end

Overloading Methods

def create_car (make = :Ford,
model = get_default_model(make),
colour)
…
end
create_car('red' )

Method Parameters

def produce_student(name, *subjects)
…
end
produce_student('June Black', 'Chemistry',
'Maths', 'Computing' )
subject_list = ['Chemistry', 'Maths', 'Computing']
produce_student('June Black', *subject_list)

Variable Length Param List

class Meteor
attr_accessor :speed
def initialize()
@speed = 0
end
def +(amt)
@speed += amt
end
def -(amt)
@speed > amt ? (@speed -= amt) : (@speed = 0)
end
end

Operators

class Roman
def self.method_missing name, *args
roman = name.to_s
roman.gsub!("IV", "IIII")
roman.gsub!("IX", "VIIII")
roman.gsub!("XL", "XXXX")
roman.gsub!("XC", "LXXXX")
(roman.count("I") +
roman.count("V") * 5 +
roman.count("X") * 10 +
roman.count("L") * 50 +
roman.count("C") * 100)
end
end

Method
Missing

handlers = { up_arrow: :tilt_up,
down_arrow: :tilt_down,
left_arrow: :turn_left,
right_arrow: :turn_right}
ship.__send__(handlers[input])

Send

•
•
•
•
•
•

Alter the WindowsComputer class you created in the
last exercise to make the name parameter optional
Try creating an instance with and without a name
value
Add a mandatory attribute called owner to the class
and alter initialize to set it.
Try creating a new instance with no, 1 and 2
parameter values. What happens?
add a method display_details to output the name
and owner of the machine and try calling it using
__send__
now make display_details private and try calling it
directly and using __send__. Notice anything odd?

Exercises

def block_example
puts 'Optional block example.'
if block_given?
yield "Heather"
else
puts 'No block. Very Empty'
end
puts 'End of example'
end

Blocks

def with_timing
start = Time.now
if block_given?
yield
puts 'Time taken:
#{Time.now - start}'
end
end

Blocks

def add_numbers(x, y)
x+y
end
alter the above method to accept a block and
execute it if one is supplied. Call it with a block to
provide debug i.e. displaying the method name
and values passed

Exercises

Test
Driven
Development
Behaviour
Driven
Development

require 'minitest/autorun'
require '../lib/People'
class TestEmployee < MiniTest::Unit::TestCase
def setup
@employee = Employee.new
end
def test_employer
assert_equal "Kainos", @employee.employer
end

end

MiniTest

require "minitest/autorun"
describe Employee do
before do
@employee = Employee.new
end
describe "when asked for an employer" do
it "must provide one" do
@employee.employer.must_equal "Kainos"
end
end
end

MiniTest

# bowling_spec.rb
require 'bowling'
describe Bowling, "#score" do
it "returns 0 for all gutter game" do
bowling = Bowling.new
20.times { bowling.hit(0) }
bowling.score.should eq(0)
end
end

RSpec

# division.feature
Feature: Division
In order to avoid silly mistakes
Cashiers must be able to calculate a fraction
Scenario: Regular numbers
* I have entered 3 into the calculator
* I have entered 2 into the calculator
* I press divide
* the result should be 1.5 on the screen

Cucumber

#calculator_steps.rb

Before do
@calc = Calculator.new
end
Given /I have entered (d+) into the calculator/ do
|n|
@calc.push n.to_i
end
When /I press (w+)/ do |op|
@result = @calc.send op
end

Cucumber

Want to Learn More?
Codecademy
http://www.codecademy.com/tracks/ruby

CodeSchool
https://www.codeschool.com/paths/ruby

Seven Languages in Seven Weeks
pragprog.com/book/btlang/seven-languages-in-seven-weeks

Want to Learn More?
Programming Ruby

pragprog.com/book/ruby/programming-ruby
First edition available for free online at
http://ruby-doc.com/docs/ProgrammingRuby/

Ruby Koans
http://rubykoans.com

Pluralsight

Intro to ruby

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