A quick Ruby Tutorial

1. A quick Ruby Tutorial COMP313 Source: Programming Ruby, The Pragmatic Programmers’ Guide by Dave Thomas, Chad Fowler, and Andy Hunt

2. Ruby • Invented by Yukihiro Matsumoto, “Matz” • 1995 • Fully object-oriented • alternative to Perl or Python

3. How to run • Command line: ruby <file> • Interactive: irb • Resources: • see web page • man ruby

4. Simple method example def sum (n1, n2) n1 + n2 end sum( 3 , 4) => 7 sum(“cat”, “dog”) => “catdog” load “fact.rb” fact(10) => 3628800

5. executable shell script #!/usr/bin/ruby print “hello world\n” or better: #!/usr/bin/env ruby make file executable: chmod +x file.rb

6. Method calls "gin joint".length → 9 "Rick".index("c") → 2 -1942.abs → 1942 Strings: ‘as\n’ => “as\\n” x = 3 y = “x is #{x}” => “x is 3”

7. Another method definition def say_goodnight(name) "Good night, #{name}" end puts say_goodnight('Ma') produces:Good night, Ma

8. Name conventions/rules • local var: start with lowercase or _ • global var: start with $ • instance var: start with @ • class var: start with @@ • class names, constant: start uppercase following: any letter/digit/_ multiwords either _ (instance) or mixed case (class), methods may end in ?,!,=

9. Naming examples • local: name, fish_and_chips, _26 • global: $debug, $_, $plan9 • instance: @name, @point_1 • class: @@total, @@SINGLE, • constant/class: PI, MyClass, FeetPerMile

10. Arrays and Hashes • indexed collections, grow as needed • array: index/key is 0-based integer • hash: index/key is any object a = [ 1, 2, “3”, “hello”] a[0] => 1 a[2] => “3” a[5] => nil (ala null in Java, but proper Object) a[6] = 1 a => [1, 2, “3”, “hello”, nil, nil, 1]

11. Hash examples inst = { “a” => 1, “b” => 2 } inst[“a”] => 1 inst[“c”] => nil inst = Hash.new(0) #explicit new with default 0 instead of nil for empty slots inst[“a”] => 0 inst[“a”] += 1 inst[“a”] => 1

12. Control: if example if count > 10 puts "Try again" elsif tries == 3 puts "You lose" else puts "Enter a number" end

13. Control: while example while weight < 100 and num_pallets <= 30 pallet = next_pallet() weight += pallet.weight num_pallets += 1 end

14. nil is treated as false while line = gets puts line.downcase end

15. Statement modifiers • useful for single statement if or while • similar to Perl • statement followed by condition: puts "Danger" if radiation > 3000 square = 2 square = square*square while square < 1000

16. builtin support for Regular expressions /Perl|Python/ matches Perl or Python /ab*c/ matches one a, zero or more bs and one c /ab+c/ matches one a, one or more bs and one c /\s/ matches any white space /\d/ matches any digit /\w/ characters in typical words /./ any character (more later)

17. more on regexps if line =~ /Perl|Python/ puts "Scripting language mentioned: #{line}" end line.sub(/Perl/, 'Ruby') # replace first 'Perl' with 'Ruby' line.gsub(/Python/, 'Ruby') # replace every 'Python' with 'Ruby’ # replace all occurances of both ‘Perl’ and ‘Python’ with ‘Ruby’ line.gsub(/Perl|Python/, 'Ruby')

18. Code blocks and yield def call_block puts "Start of method" yield yield puts "End of method" end call_block { puts "In the block" }produces: Start of method In the block In the block End of method

19. parameters for yield def call_block yield("hello",2) end then call_block { | s, n | puts s*n, "\n" } prints hellohello

20. Code blocks for iteration animals = %w( ant bee cat dog elk ) # create an array # shortcut for animals = {“ant”,”bee”,”cat”,”dog”,”elk”} animals.each {|animal| puts animal } # iterate produces: ant bee cat dog elk

21. Implement “each” with “yield” # within class Array... def each for every element # <-- not valid Ruby yield(element) end end

22. More iterations [ 'cat', 'dog', 'horse' ].each {|name| print name, " " } 5.times { print "*" } 3.upto(6) {|i| print i } ('a'..'e').each {|char| print char } [1,2,3].find { |x| x > 1} (1...10).find_all { |x| x < 3}

23. I/O • puts and print, and C-like printf: printf("Number: %5.2f,\nString: %s\n", 1.23, "hello") #produces: Number: 1.23, String: hello #input line = gets print line

24. leaving the Perl legacy behind while gets if /Ruby/ print end end ARGF.each {|line| print line if line =~ /Ruby/ } print ARGF.grep(/Ruby/)

25. Classes class Song def initialize(name, artist, duration) @name = name @artist = artist @duration = duration end end song = Song.new("Bicylops", "Fleck", 260)

26. override to_s s.to_s => "#<Song:0x2282d0>" class Song def to_s "Song: #@name--#@artist (#@duration)" end end s.to_s => "Song: Bicylops--Fleck (260 )”

27. Some subclass class KaraokeSong < Song def initialize(name, artist, duration, lyrics) super(name, artist, duration) @lyrics = lyrics end end song = KaraokeSong.new("My Way", "Sinatra", 225, "And now, the...") song.to_s → "Song: My Way--Sinatra (225)"

28. supply to_s for subclass class KaraokeSong < Song # Format as a string by appending lyrics to parent's to_s value. def to_s super + " [#@lyrics]" end end song.to_s → "Song: My Way--Sinatra (225) [And now, the...]"

29. Accessors class Song def name @name end end s.name => “My Way” # simpler way to achieve the same class Song attr_reader :name, :artist, :duration end