Introduction to Ruby. Part I

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1 Introduction to Ruby Sebastian Fischer Part I Data Numbers, Strings, Ranges, Arrays/Hashes Control Branching, Loops, Iterators

2 Numbers >> 42 => 42 >> -17 => -17 >> 1.23 => 1.23 >> 4.56e7 => >> 2.34e-4 => >> 2.34>0 => true >> 17e-1.round => 2 >> 17/4 => 4 >> 17./ 4 => 4 Strings >> hello = "hello" => "hello" >> world = "world" => "world" >> hello = "#{hello} #{world}!" => "hello world!" >> hello.chop! => "hello world" >> hello => "hello world"

3 Escape >> "hello\nworld!" => "hello\nworld!" >> 'hello\nworld!' => "hello\\nworld!" >> "hello#{17+4}world!" => "hello21world!" >> 'hello#{17+4}world!' => "hello\#{17+4}world!" Regular Expressions >> hello =~ /\s\w+/ => 5 >> hello[5,6] => " world" >> hello[5..10] => " world" >> hello.gsub!(/\s\w+/,'\&!') => "hello world!" >> hello => "hello world!"

4 Ranges >> 1..3 => 1..3 >> (1..3).first => 1 >> (1..3).last => 3 >> (1..3).member? 3 => true >> (1..3).member? 4 => false >> (1..3).entries => [1, 2, 3] Arrays >> a = [1,true,"huh?"] => [1, true, "huh?"] >> a[2] => "huh?" >> a.length => 3 >> a + [42] => [1, true, "huh?", 42] >> a * 2 => [1, true, "huh?", 1, true, "huh?"]

5 Arrays >> (a*2)[2..4] => ["huh?", 1, true] >> (a*2)[2,3] => ["huh?", 1, true] >> a[-1] => "huh?" >> a[-2] => true Hashes >> h = { 1 => true, "huh?" => 2.34 } => {1=>true, "huh?"=>2.34} >> h[1] => true >> h["huh?"] => 2.34 >> h[true] => nil >> h[true] = 42 => 42 >> h => {true=>42, 1=>true, "huh?"=>2.34}

6 Symbols >> :foo => :foo >> :foo.to_i => >> :foo.id2name => "foo" >> "foo".to_sym => :foo Data Numbers Strings, Regular Expressions Ranges Arrays Hashes

7 If, Unless >> if 3>0 then 42 else 87 => 42 >> 42 if 3>0 => 42 >> unless 3>0 then 42 else 87 => 87 >> 87 unless 3>0 => nil Case >> case i >> when 1, 2..5 >> "one to five" >> when >> "six to ten" >> => "six to ten" >> case "abcdef" >> when "abc","def" >> "abc or def" >> when /def/ >> "includes def" >> => "includes def" >> (6..10) === 8 => true >> /def/ === "abcdef" => true

8 While >> fac5 = 1; n = 1 => 1 >> while n <= 5 >> fac5 = fac5 * n >> n = n+1 >> ; fac5 => 120 While while (<condition>) { label_redo: <body> label_next: } label_break:

9 Until >> fac5 = 1; n = 1 => 1 >> until n > 5 >> fac5 = fac5 * n >> n = n+1 >> ; fac5 => 120 For/in >> fac5 = 1; >> for n in 1..5 >> fac5 = fac5 * n >> ; fac5 => 120

10 Iterators >> fac5 = 1 => 1 >> (1..5).each { n fac5 = fac5 * n } => 1..5 >> fac5 => 120 Iterators >> "hello".each_byte { b puts b } => "hello" >> "hello\nworld!".each { l puts l } hello world! => "hello\nworld!"

11 Iterators >> (1..3).each{ n print n } 123=> 1..3 >> [1,2,3].each{ n print n } 123=> [1, 2, 3] >> h.each{ k,v puts "#{k} => #{v}" } true => 42 1 => true => {true=>42, 1=>true} Iterators >> 3.times { puts "hello" } hello hello hello => 3 >> 1.upto(3) do n?> puts n >> => 1

12 Control if, unless case while, until, for/in Iterators Part II Classes and Objects Inheritance, Methods, Access Control Accessor Methods Modules

13 Classes >> class Person >> def initialize name = name >> >> >> me = Person.new "Sebastian" => Classes class Man < Person def initialize name super = :male class Woman < Person def initialize name super = :female

14 Objects >> me = Man.new "Sebastian" >> me.@name SyntaxError: compile error >> me.name NoMethodError: undefined method `name' Accessor Methods class Person def def = n class Person attr_accessor :name

15 Accessor Methods >> me.name => "Sebastian" >> me.name = "Horst" => "Horst" >> me Modules module WithGer attr_reader :ger class Man include WithGer class Woman include WithGer

16 Reader Methods >> me.ger => :male >> me.ger = :female NoMethodError: undefined method `ger=' Singleton Methods >> def me.ger=(g) = g >> => nil >> me.ger = :female => :female >> me

17 Modules module Student = 0 attr_reader :nr def += 1 private :next_nr Mixin class MaleStudent < Man include Student def initialize name super = next_nr class FemaleStudent < Woman include Student...

18 Accessor Methods >> axel = MaleStudent.new "Axel" @ger=:male> >> rita = FemaleStudent.new "Rita" @ger=:female> >> axel.ger => :male >> rita.nr => 2 Exting Classes >> class Integer >> def fact >> return 1 if self==0 >> self * (self-1).fact >> >> => nil >> 5.fact => 120

19 Class Hierarchies >> 5.class => Fixnum >> Fixnum.superclass => Integer >> Integer.superclass => Numeric >> Numeric.superclass => Object >> Object.superclass => nil Classes are Objects >> Integer.class => Class >> Class.class => Class >> Class.superclass => Module >> Module.class => Class >> Module.superclass => Object

20 Global Functions >> def square x >> x*x >> => nil >> self.methods.select { m m =~ /sq/ } => ["square"] >> 42.methods.select { m m =~ /sq/ } => ["square"] >> "".square 7 => 49 Scope >> ["a","b","c"].each { str print str} abc=> ["a", "b", "c"] >> str NameError: undefined local variable or method `str' for main:object >> str = "z" => "z" >> ["a","b","c"].each { str print str} abc=> ["a", "b", "c"] >> str => "c"

21 Variables Constants uppercase: Math::PI Global Variables dollar sign: $PROGRAM_NAME Constants >> Object.constants => ["IO", "Student",...] >> Student.constants => [] >> WithGer.constants => []

22 Prettier Objects module Student def inspect str = "Student: #{nr}" str += ", Name: #{name}" \ if respond_to? :name str += ", Ger: #{ger}" \ if respond_to? :ger str Prettier Objects >> axel => Student: 1, Name: Axel, Ger: male >> puts axel #<MaleStudent:0x365470> => nil

23 Prettier Objects >> class Person >> def to_s; inspect >> >> puts axel Student: 1, Name: Axel, Ger: male => nil Exceptions class Person def name=(n) raise "name must not be empty!" \ if = n >> me.name = "" RuntimeError: name must not be empty!

24 Exceptions >> begin?> me.name = "" >> puts 'name was set to ""' >> rescue >> puts "could not set name" >> ensure?> puts "finished" >> could not set name finished => nil Useful Stuff >> 5.f 5.floor 5.freeze 5.frozen? 5.fact >> 5.f >> 5.methods => ["%", "inspect",...]

25 Useful Stuff $ ri Array#each Array#each array.each { item block } -> array Calls _block_ once for each element in _self_, passing that element as a parameter.... Ruby will teach you to express your ideas through a computer. You will be writing stories for a machine.

26 Part III Object#s Method#call Kernel#eval Object#s >> "hello world".s :length => 11 >> "hello world".s "length" => 11 >> "hello".s :<<, " world" => "hello world"

27 Method#call >> "hello world".method(:length).call => 11 >> app = "hello".method :<< => #<Method: String#<<> >> app.call(" world") => "hello world" Kernel#eval >> eval '"hello world".length' => 11 >> eval '"hello" << " world"' => "hello world" >> eval 'system "rm *"'

28 Module#class_eval class Module def my_attr_reader sym class_eval "def #{sym}()" << " def my_attr_writer sym class_eval "def #{sym}=(v)" << " Attribute Accessors class Klass my_attr_reader :a my_attr_reader :b my_attr_writer :b def

29 Attribute Accessors >> klass = Klass.new => >> klass.a => 42 >> klass.b = 17 => 17 >> klass.b => 17

Ruby, with foxes. Ruby, cont d. Warning. why's (poignant) Guide to Ruby

Ruby, with foxes. Ruby, cont d. Warning. why's (poignant) Guide to Ruby O Ruby, cont d n O Ruby, with foxes n why's (poignant) Guide to Ruby Ruby explained through humorous and more or less irrelevant stories about foxes, elfs, cats and others Warning If I was put off Ruby