1-basics.md

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Basics

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@@@ruby
# obligatory hello world 
p "hello, world"

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ruby -e 'p "hello, world"'

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@@@ruby
name = 'Anthony'
p "hello, #{name}"

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@@@ruby
# everything is an object
# and objects have methods
2.even?                     # returns true
1.2.ceil                    # returns 2
"Anthony knows Ruby".length # returns 18

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@@@ruby
# method names
word = "   example  "

word.strip    # returns "example"
p word        # prints "   example  "
word.strip!   # returns "example"
p word        # prints "example"

File.readable? '/etc/password'
File.readable? '/tmp'

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@@@ruby
# methods can be chained
# returns ['Ruby', 'knows', 'Anthony']
"Anthony knows Ruby".split.reverse

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@@@ruby
# blocks
[1, 2, 3, 4].map { |i| i ** 2 } # [1, 4, 9, 16]

5.times { p 'ohai' }    # prints "ohai" 5 times

0.upto(5) { |n| p n }   # prints from 0 to 5

(0..5).each { |n| p n } # also prints from 0 to 5

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#Classes and Objects#

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@@@ ruby
# defining a class
class Person
end

# constructing an instance
person = Person.new

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@@@ruby
# initializer, instance variables, methods
class Person
  def initialize(name)
    @name = name
  end
  def name
    @name
  end
end

person = Person.new('Anthony')
person.name

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@@@ruby
# attr_reader
class Person
  attr_reader :name
  def initialize(name)
    @name = name
  end
end

person = Person.new('Anthony')
person.name

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@@@ruby
# multiple attr_reader
class Person
  attr_reader :name
  attr_reader :height
  def initialize(name)
    @name = name
  end
end

person = Person.new('Anthony')
person.name     # returns 'Anthony'
person.height   # returns nil

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@@@ruby
# initialize with hash
class Person
  attr_reader :name, :age, :height

  def initialize(attrs={})
    @name = attrs[:name]
    @age = attrs[:age]
    @height = attrs[:height]
  end
end

person = Person.new(
  :name => 'Anthony', 
  :height => 180
)
person.name       # returns 'Anthony'
person.height     # returns 180
person.age        # returns nil
person.age = 34   # raises an error

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@@@ruby
# attr_accessor
class Person
  attr_accessor :name, :age, :height

  def initialize(attrs={})
    @name = attrs[:name]
    @age = attrs[:age]
    @height = attrs[:height]
  end
end

person = Person.new(
  :name => 'Anthony', 
  :height => 180
)
person.age = 34
person.age        # returns 34

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@@@ruby
# set variable values on one line
# logic in methods
class Person
  attr_accessor :name, :age, :height

  def initialize(attrs={})
    @name, @age, @height = attrs[:name], 
      attrs[:age], attrs[:height]
  end

  def height_in_inches
    height * 0.39370079
  end
end

person = Person.new(:height => 180)
person.height_in_inches # returns 70.8661422

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@@@ruby
# constants
class Person
  attr_accessor :name, :age, :height

  def initialize(attrs={})
    @name, @age, @height = attrs[:name], 
      attrs[:age], attrs[:height]
  end

  CM_TO_INCHES = 0.39370079
  def height_in_inches
    height * CM_TO_INCHES
  end
end

person = Person.new(:height => 180)
person.height_in_inches # returns 70.8661422

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@@@ruby
# class methods
class Person
  @people = {}
  def initialize(name)
    @name = name
  end
  def self.find_or_create(name)
    @people[name] ||= Person.new(name)
  end
end

# Returns a new Person
Person.find_or_create('Anthony')
# Returns a new Person
Person.find_or_create('John')
# Returns Person named Anthony from above
Person.find_or_create('Anthony')