Ruby 101: Syntax, Methods, Data Types & Control Flow

Ruby 101
1
Thursday, April 18, 13

Topics
• Ruby Syntax
• Methods/Functions
• DataTypes
• Control Flow
• Exceptions
2

Ruby Syntax
3

Ruby Syntax
• indent 2 spaces, no tabs
• CamelCase for class names
• snake_case_for methods and variables
• ﬁlenames always snake case
user_setting.rb
class UserSetting
def update_from_params(params)
end
def save
end
end 4

Ruby Syntax
• comments start with #
• multi-line =begin =end
# one line comment
=begin
name = "Bob"
address = "123 street"
city = "Any Town"
=end
5

parentheses optional
(mostly!)
need them here
else will an OR here
Document.new "The Ruby Way", "Hal Fulton"
Document.new("The Ruby Way", "Hal Fulton")
event_date.to_s :short
event_date.to_s(:short)
if name.blank?
puts "Hi nobody"
end
if (name.blank? || (name == "bob"))
if name.blank? || (name == "bob")
if name.blank? || name == "bob"
6

one more thing about
parentheses
class User
def status
#blah blah
end
end
class User
def status()
#blah blah
end
end
always
never
7

Variables
8
$global_variable
@@class_variable
@instance_variable
CONSTANT

String Interpolation
vs String Concatenation
10.times { |n| puts "the number is #{n}" }
String Interpolation, plus reads better
10.times { |n| puts "the number is" + n }
String concatenation, slow-er!
plus calls to_s if not a string
9

• code style
• variable/class style
• comments
• role of parentheses
• variables
• string interpolation
10
Learned about Ruby Syntax

Methods
11
functions usually called methods

Method Return Values
12
def format_name(user)
return "#{user.first.capitalize} #{user.last.capitalize}"
end
def format_name(user)
"#{user.first.capitalize} #{user.last.capitalize}"
end
Last line of function is implicit return

methods with ? !
13
def validate_user?(user)
if user.first.present? && user.last.present?
true
else
false
end
end
def promote_user!(user, level)
user.access = level
user.save
end

methods with ?
14
> "classified ventures".include?("class")
=> true
> "classified ventures".include?("blah")
=> false
Use ? as part of the method name if it
returns a boolean

Using !
15
> company = "classified ventures"
=> "classified ventures"
> company.upcase
=> "CLASSIFIED VENTURES"
> company
=> "classified ventures"
> company.upcase!
> company

Learned about
• ! methods
• ? methods
• return value
16

Data Types
Everything is an object
no such idea as “primitives”
17

Strings
> company = "Classified Ventures"
=> "Classified Ventures"
> company.length
=> 19
> company.reverse
=> "serutneV deifissalC"
> company.upcase
> company.start_with?("Class")
=> true
> company.start_with?("Goo")
=> false
18

Symbols
> :first
=> :first
> :first.class
=> Symbol
Commonly used in Hashes
19

Whats the difference?
> "hello".object_id
=> 70312121540820
> "hello".object_id
=> 70312126306720
> :first.object_id
=> 32488
> :first.object_id
=> 32488
20

FixNum,
BigNum,Booleans
> 1.class
=> Fixnum
> 10000000000000000000000000.class
=> Bignum
> 3.14.class
=> Float
> true.class
=> TrueClass
> false.class
=> FalseClass
21

Arrays
fruits = ['apple', 'orange', 'pear']
fruits = %w(apple orange pear)
=> ['apple', 'orange', 'pear']
a = Array.new(5)
=> [nil, nil, nil, nil, nil]
a = Array.new(5, "--")
=> ["--", "--", "--", "--", "--"]
22

Hashes
default value if key is not found
fruits = {:apple => 5, :orange => 4, :pear => 1}
fruits = { apple: 5, orange: 4, pear: 1 }
fruits[:apple]
=> 5
z = {} #default is nil
a = Hash.new( "--" ) #default is “--”
z[:blah]
=> nil
a[:blah]
=> "--"
Ruby 1.9
23

Struct
24
Crumb = Struct.new(:name, :value)
=> Crumb
home = Crumb.new("Home", "/")
=> #<struct Crumb name="Home", value="/">
home
=> #<struct Crumb name="Home", value="/">
> home.name
=> "Home"
> home.value
=> "/"

Ranges
25
> 1..10
=> 1..10
> (1..10).class
=> Range
> (1..10).to_a (creates array)
=> [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
> (1...10).to_a
=> [1, 2, 3, 4, 5, 6, 7, 8, 9]
two dots includes end point
three dots does not include end point

Learned about Datatypes
• Strings
• Symbols
• FixNum, BigNum
• Booleans
• Array
• Hash
• Struct
• Ranges
26

Practice
• www.rubykoans.com
• http://www.zenspider.com/
Languages/Ruby/QuickRef.html
27

Classes
class Document
attr_accessor :title, :author, :content
def initialize(title, author, content)
@title = title
@author = author
@content = content
end
end
@var is an instance variable
access it as @var inside class
28
constructor

attr_accessor
makes getters and setters
class Document
# setter
def title=(title)
@title = title
end
# getter
def title
@title
end
class Document
attr_accessor :title
end
same result
also attr_reader and attr_writer
29

Example Class
class Document
attr_accessor :title, :author
def initialize(title, author)
@title = title
@author = author
end
def words
@content.split
end
def self.supported_file_types
%w(pdf jpg gif doc)
end
end
doc = Document.new("The Ruby Way", "Fulton")
doc.words
Document.supported_file_types
30
instance method
class method

Learned about
• class constructors
• getters/setters
• instance methods
• static methods
31

Control Flow
32

Code Blocks
10.times { |n| puts "the number is #{n}" }
10.times do |n|
puts "the number is #{n}"
better_for_longer_blocks(n)
end
33
item for each iteration is n

if / unless
if not @readonly
doc.write(text)
end
unless @readonly
doc.write(text)
end
unless @readonly
doc.write(text)
else
log.warn("attempt to write to readonly file")
end
doc.write(text) unless @readonly
bad
good
good
bad
34

for / each
fruits = ['apple', 'orange', 'pear']
for fruit in fruits
puts fruit
end
fruits.each do |fruit|
puts fruit
end
bad
good
35

while loops
36
i = 0
while i < 5
puts i
i += 1
end
i = 0
until i == 5
puts i
i += 1
end
puts i += 1 until i == 5

Exceptions
37
class Name
# Define default getter method, but not setter method.
attr_reader :first
# When someone tries to set a first name, enforce rules about it.
def first=(first)
if first.blank?
raise ArgumentError.new('Everyone must have a first name.')
end
@first = first.capitalize
end
end
def edit
name = Name.new
name.first = params[:name]
rescue ArgumentError => e
log.error("Validation Error #{e.message}")
end

Covered Control Flow
• if/unless
• for/each
• while loops
• exceptions
38

Ruby 101: Syntax, Methods, Data Types & Control Flow

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