Schipplock - Ruby Quickstart

Ruby Quickstart

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Ruby entered my brain in 2004 when I bought a book about it. I was curious but obviously not curious enough to learn it so I basically don’t know a shit anymore and I’m sure I don’t even read the whole book (as always, hello scala!).

However, ruby is not so special if you already know another programming or scripting language and I started becoming interested again, so here we are:

assigning variables

my_super_cool_variable = "some string value"
puts my_super_cool_variable
print "6^2 = "+(6**2).to_s

Oh, see, converting between string and integer values is actually very easy. Just append .to_i or .to_s and you are done.

Arrays

cars = ["Audi","BMW","Mercedes","Lexus"]
p cars
puts cars[0]
puts cars
puts cars.length
puts cars.reverse
puts cars[0..cars.length]

for run in (0..cars.length)
  puts cars[run]
end

Add elements to your array

cars = ["Audi","BMW","Mercedes","Lexus"]
p cars
cars << "Saab"
p cars

getting user input

car = gets
print car

reading a file

file_contents = File.read("/etc/resolv.conf")
print file_contents

writing to a file

print "enter your first name: "
file_handle = File.new("/tmp/foobar", "w")
first_name = gets
file_handle.puts first_name
file_handle.close

It asks for your first name and writes it to /tmp/foobar. “cat” the file after executing this script. Your name will be in it. Easy peasy!

simple functions / methods

def foobar
  puts "foobar"
end

foobar # prints "foobar\n"

def greet(firstname, lastname)
  puts "Welcome "+firstname+" "+lastname
end

greet("Andreas","Schipplock")

def greet(*family)
  p family
end

greet("Oma","Opa","Tante","Cousine")

simple prototype based object orientation

car = Object.new

def car.drive 
 puts "driving along the road"
end

def car.speedup(speed)
  puts "speeding up to "+speed.to_s+" km/h"
end

def car.mileage
  return 120000
end

def car.started?
  return false
end

def car.id
  return self.object_id
end

def car.add_features(*features)
  p features # p = print for arrays
end

def car.default_climate_value(temperature=20)
  return temperature
end

car.drive
car.speedup(140)
puts car.mileage.to_s
puts car.started?.to_s
puts car.id.to_s
car.add_features("air cooling", "automatic transmission", "foobar")
puts car.default_climate_value.to_s
puts car.default_climate_value(25).to_s

if car.respond_to?("turn_turbo_on")
  car.turn_turbo_on
else
  puts "sorry, this car doesn't have a turbo"
end

print "what do you want the car to do now? -> "
method = gets.chomp

if car.respond_to?(method)
  car.send(method)
else
  puts "sorry, the car can't do that"
end

executing this script could look like this:

andreas_schipplock@andreas:~/projects/ruby$ ruby1.9.1 c2f.rb 
driving along the road
speeding up to 140 km/h
120000
false
74485320
["air cooling", "automatic transmission", "foobar"]
20
25
sorry, this car doesn't have a turbo
what do you want the car to do now? -> drive
driving along the road
andreas_schipplock@andreas:~/projects/ruby$

a simple class

class Car
  def speedup
    return true
  end
end

audi = Car.new
if audi.speedup
  puts "yo, dawg, I'm speeding up"
else
  puts "eh, mother*, I'm an old lady"
end

a little more advanced example of a class

class Car
  def initialize(build_year,mileage)
    @build_year = build_year
    @mileage = mileage
    @ready = true
  end

  def speedup(speed)
    @current_speed = speed
  end

  def current_speed
    return @current_speed
  end

  def ready?
    return @ready
  end

  def age
    return (Time.new).year - @build_year
  end

  def mileage
    return @mileage
  end
end

audi = Car.new(1989,245000)

if audi.ready?
  audi.speedup(140)
  puts audi.current_speed
  audi.speedup(220)
  puts audi.current_speed
  puts "age: "+audi.age.to_s
  puts "mileage: "+audi.mileage.to_s
end

The variables with the @-sign are properties or instance variables that are available inside the class. The example demonstrates their state inside the class. The “initialize” method is the constructor and is called whenever you create a new instance “audi = Car.new”.

get and setter methods

class Car
  def initialize(mileage)
    @mileage = mileage
  end

  def mileage=(miles)
    @mileage = miles
  end

  def mileage
    @mileage
  end
end

audi = Car.new(245000)
puts "old mileage: "+audi.mileage.to_s
audi.mileage = 246000
puts "new mileage: "+audi.mileage.to_s

You can shorten that:

class Car
  attr_reader :mileage
  attr_writer :mileage

  def initialize(mileage)
    @mileage = mileage
  end
end

audi = Car.new(245000)
puts "old mileage: "+audi.mileage.to_s
audi.mileage = 246000
puts "new mileage: "+audi.mileage.to_s

And even shorter…

class Car
  attr_accessor :mileage

  def initialize(mileage)
    @mileage = mileage
  end
end

audi = Car.new(245000)
puts "old mileage: "+audi.mileage.to_s
audi.mileage = 246000
puts "new mileage: "+audi.mileage.to_s

“attr_reader :mileage” unfolds to:

def mileage
  @mileage
end

“attr_writer :mileage” unfolds to

def mileage=(miles)
  @mileage = miles
end

“attr_accessor :mileage” unfolds to

def mileage=(miles)
  @mileage = miles
end

def mileage
  @mileage
end

Inheritance

class Car
  def type
    @type = "rwd"
  end
end

class Audi < Car
  def type
    @type = "awd"
  end
end

my_car = Audi.new
puts my_car.type

Outputs “awd”.

Inheritance with constants

class Car
  TYPES = ["AWD", "RWD", "FWD"]
  def type
    @type = self::TYPES[1]
  end
end

class Audi < Car
  def type
    @type = Car::TYPES[0]
  end
end

my_car = Audi.new
puts my_car.type

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