Learning Ruby

1. Methods Learning Ruby

2. Methods • We’ve seen several so far: puts, gets, chomp, to_s, and even +, -, * and / • Usually use dot notation • 5 + 5 is really just a shortcut way of writing 5.+ 5 • ‘pit ’ * 5

3. String methods lineWidth = 50 puts( 'Old Mother Hubbard'.center(lineWidth)) lineWidth = 40 str= '--> text <--' puts str.ljustlineWidth #parens are optional

4. Random Numbers rand -> float greater than or equal to 0.0 and less than 1.0. rand(5) -> int in range 0..4 srand 1776 gives the random number generator a seed puts(Math::PI) #:: is scope resolution

5. Defining own methods def sayMoonumberOfMoos puts 'mooooooo...'*numberOfMoos end # Note local variables def doubleThis num numTimes2 = num*2 puts num.to_s+' doubled is '+numTimes2.to_s end doubleThis 44 puts numTimes2.to_s # undefined variable

6. Makes local copy def littlePestvar var = nil puts 'HAHA! I ruined your variable!' end var = 'You can\'t even touch my variable!‘ littlePestvar puts var

7. Ruby Methods are Easy! def addThem( first, second ) first + second The value of the last statement in the method is value returned, but you can also use “return” end # of addThem. puts addThem( 23, 6 )  29 def addThemAll( first, *rest )  variable number of parameters tot=first rest.each{|val| tot +=val} tot  or return tot end paddThemAll( 1, 2, 3, 4, 5, 6, 7 )  28

8. Scope • Local variables (begin with either an underscore or a lower case letter) and are local to the code construct in which they are declared. For example, a local variable declared in a method or within a loop cannot be accessed outside of that loop or method. • Global variables (begin with $) are accessible from anywhere in the Ruby program, regardless of where they are declared. • A class variable (begins with @@) is shared amongst all instances of a class. • Instance variables (begin with @) are similar to Class variables except that their values are local to specific instances of an object.

9. Yield – calls provided block def yup yield yield yield end yup {puts "where is the beef?"} yield: calls the provided block where is the beef? where is the beef? where is the beef?

10. At Seats: what is output? def test puts "You are in the method" yield puts "You are again back to the method" yield end test {puts "You are in the block"}

11. Yield – reusing code (block can have parameters) def triple(max) yield 3*max end triple(8) { |x| print x, ", “} ->24

12. Yield – reusing code what is output? def cubes(max) i=1 while i < max yield i**3 i += 1 end end cubes(8) { |x| print x, ", "} sum = 0 cubes(8) { |y| sum += y} print "\nsum=",sum product = 1 cubes(8) { |z| product *= z} print "\nproduct=",product Scope of block passed is calling block not called block. sum is NOT known inside cubes but is known inside code block.

13. Yield – reusing code (output) def cubes(max) i=1 while i < max yield i**3 i += 1 end end cubes(8) { |x| print x, ", "} sum = 0 cubes(8) { |y| sum += y} print "\nsum=",sum product = 1 cubes(8) { |z| product *= z} print "\nproduct=",product 1, 8, 27, 64, 125, 216, 343, sum=784 product=128024064000 Scope of block passed is calling block not called block. sum is NOT known inside cubes but is known inside code block.

14. Yield def compute( what ) if block_given? yield( what ) else what end # of if. end # of compute puts compute( 22 ) puts compute ( 11 ) { |num| num*num } puts compute (4 ) { |num| num+num } block_given? is built-in Return value is last thing executed 22 121 8

15. This is how each could be implemented via yieldself – current class “this” class Array # Note how I can extend the functionality of built-in classes def my_each() 0.upto(length-1) do |i| yield self[i]  call to provided code with my ith element end return self  if want to use in assign statement or nest calls end end puts "Array\n" t = ["quit", "felt", "worry", "smith", "white", "abandon", "fish", "this", "oboe"] t.my_each{|i| print i, "\n" } p t.my_each{|i| print "The element is ", i, "\n" }.sort! -> prints elements then ["abandon", "felt", "fish", "oboe", "quit", "smith", "this", "white", "worry"]

16. What does this do? class NumericSequences def fib(limit) yield 0, 0 yield 1, 1 prev = 0 curr = 1 i=2 while (i <= limit) new = prev + curr yield i, new prev = curr curr = new i = i+1 end end end g = NumericSequences.new-> Creates instance of class g.fib(10) {|i,x| print "The #{i}thnumber: #{x}\n"}

17. Using yield to print Fibonacci numbers class NumericSequences def fib(limit) yield 0, 0 yield 1, 1 prev = 0 curr = 1 i=2 while (i <= limit) new = prev + curr yield i, new prev = curr curr = new i = i+1 end end end g = NumericSequences.new g.fib(10) {|i,x| print "The #{i}th Fibonacci number: #{x}\n"} The 0th Fibonacci number: 0 The 1th Fibonacci number: 1 The 2th Fibonacci number: 1 The 3th Fibonacci number: 2 The 4th Fibonacci number: 3 The 5th Fibonacci number: 5 The 6th Fibonacci number: 8 The 7th Fibonacci number: 13 The 8th Fibonacci number: 21 The 9th Fibonacci number: 34 The 10th Fibonacci number: 55  allows two arguments to be used

18. Return multiple values def give_back ( a, *b ) return a end # of give_back. pgive_back( 10 ) pgive_back( 10, 11 ) def give_back2 ( a, *b ) return a, b end first, rest = give_back2( 1, 2, 3, 4, 5 )

19. More ... Ruby So Far • Methods can take no arguments, a fixed number of arguments, or a variable number of parameters as arguments • The value of the last statement executed is returned by the method (unless an explicit return is used)

20. Classes • Array is a class • So is Hash

21. Passing a class def create_from_factory(factory) factory.new end obj = create_from_factory(Array)

22. At seats – what does this do? Personalized chat room model 1. require "observer" 3. class Room 4. include Observable 6. def receive(message, sender) 7. changed 8. notify_observers(message, sender) 9. end 10. end 12. class Person • def initialize(name, room) • @name, @room = name, room 15. @transcript = "" 16. @room.add_observer(self) 17. end 19. attr_reader :transcript, :name 20. 21. def update(message, sender) 22. if sender == self 23. message = "Me: #{message}\n" 24. else 25. message = "#{sender.name}: #{message}\n" 26. end 27. 28. @transcript << message 29. end 30. 31. def says(message) 32. @room.receive(message, self) 33. end 34. end