Basic Ruby Syntax

1. Basic Ruby Syntax No variable declarations sum = 0 i = 1 whilei <= 10 do sum += i*i i = i + 1 end puts "Sum of squares is #{sum}\n" Newline is statement separator do ... end instead of { ... } Optional parentheses in method invocation Substitution instring value CS 142 Lecture Notes: Ruby

2. Variable Names and Scopes foo Local variable $foo Global variable @foo Instance variable in object @@foo Class variable MAX_USERS “Constant” (by convention) CS 142 Lecture Notes: Ruby

3. Ruby String Syntax • Single quotes (only \' and \\) 'Bill\'s "personal" book' • Double quotes (many escape sequences) "Found #{count} errors\nAborting job\n" • %q (similar to single quotes) %q<Nesting works: <b>Hello</b>> • %Q (similar to double quotes) %Q|She said "#{greeting}"\n| • “Here documents” <<END First line Second line END CS 142 Lecture Notes: Ruby

4. Arrays and Hashes x = Array.new x << 10 x[0] = 99 y = ["Alice", 23, 7.3] x[1] = y[1] + y[-1] person = Hash.new person["last_name"] = "Rodriguez" person[:first_name] = "Alice" order = {"item" => "Corn Flakes", "weight" => 18} order = {:item => "Corn Flakes", :weight => 18} order = {item: "Corn Flakes", weight: 18} CS 142 Lecture Notes: Ruby

5. Ruby Statements if x < 10 then ... elsifx < 20 ... else ... end while x < 10 do ... end array = [14, 22, 34, 46, 92] for value in array do ... end CS 142 Lecture Notes: Ruby

6. Factorial deffac(x) if x <= 1 then return 1 end return x*fac(x-1) end CS 142 Lecture Notes: Ruby

7. Arguments: Defaults, Variable # definc(value, amount=1) value+amount end defmax(first, *rest) result= first for x in rest do if (x > result) then result= x end end returnresult end CS 142 Lecture Notes: Ruby

8. Keyword Arguments defcreate_widget(size, properties) ... end create_widget(6, {:id => "table22", :class => "Cart"}) create_widget(6, :id => "table22", :class => "Cart") create_widget(6, id: "table22", class: "Cart") CS 142 Lecture Notes: Ruby

9. Default, Hash, Keyword def f_default(size=10, color="black", bg="white") def f_hash(properties) def f_keyword(size:10, color:"black", bg:"white") f_default 20 #+ f_default 20, "green", "red" #+ f_default 20, bg="red" #? f_hash 20 #- f_hash({:size => 20}) #+ f_hash(:bg => "red", :color => "green", :size => 20)#+ f_hash(bg:"red", color:"green", size:20) #+ f_keyword(bg:"red", color:"green", size:20) #+ f_keyword 20, "red" #- CS 142 Lecture Notes: Ruby

10. Calling Functions def max(first, *rest) … end max(5,6) max 5,6 max (5,6) # Avoid! CS 142 Lecture Notes: Ruby

11. Symbols vs. Strings staff = ["Phil", "Firas", "JJ", "Andy"] faculty = ["Phil"] staff = [:Phil, :Firas, :JJ, :Andy] faculty = [:Phil] faculty "Phil" "Phil" with Strings "Firas" staff "JJ" "Andy" faculty :Phil with Symbols :Firas staff :JJ :Andy CS 142 Lecture Notes: Ruby

12. Equivalent Code array = [14, 22, 34, 46, 92] for value in array do print(value, "\n") end array = [14, 22, 34, 46, 92]; array.eachdo |value| print(value, "\n") end Block: code passedto method CS 142 Lecture Notes: Ruby

13. Blocks, Iterators, Yield odd_numbers(3) do |i| print(i, "\n") end defodd_numbers(count) number = 1 while count > 0 do yield(number) number += 2 count -= 1 end end Block: code passedto method Invoke method’s block CS 142 Lecture Notes: Ruby

14. Blocks: Map, Select, Reduce names = ['Vien', 'Omosola', 'Sarah'] lookup = {'Vien' => 'viendinh', 'Omosola' => 'omosolao', 'Sarah' => 'ssterman'} logins = names.mapdo |n| lookup[n] end vnames = names.selectdo |n| n[0] == 'V' end namelist = names.reducedo |sum,val| sum = sum + " and " + val end CS 142 Lecture Notes: Ruby

15. Iterators are Reusable defsum_odd(count) sum = 0 odd_numbers(count) do |i| sum += i end return sum end defodd_numbers(count) number = 1 while count > 0 do yield(number) number += 2 count -= 1 end end CS 142 Lecture Notes: Ruby

16. Simple Class class Point definitialize(x, y) @x = x @y = y end defx @x end defx=(value) @x = value end end p = Point.new(3,4) puts "p.x is #{p.x}" p.x = 44 CS 142 Lecture Notes: Ruby

17. Reduce Example (extending Array) namelist = names.ereducedo |sum,val| sum = sum + " and " + val end class Array def ereduce() sum = self[0] if (size < 2) then return sum end values =last(size - 1) values.eachdo |v| sum = yield(sum, v) end return sum end end CS 142 Lecture Notes: Ruby

18. Module Examples module FileSaver def FileSaver::try_saving_file(input, dir, name) … end end require 'file_saver.rb' FileSaver::try_saving_file "Test", "./", "test.txt" module ConfigurationParams ROOT_DIR = "/home/pal" USER_NAME = "pal" end CS 142 Lecture Notes: Ruby

19. ereduceMixin module EReduce def ereduce() sum = self[0] if (size < 2) then return sum end values =last(size - 1) values.eachdo |v| sum = yield(sum, v) end return sum end end class Array include EReduce end CS 142 Lecture Notes: Ruby

20. Mixin Example New methods available in MyClass: min, max, sort, map, select, ... classMyClass include Enumerable ... defeach ... end def<=> ... end end CS 142 Lecture Notes: Ruby

21. Simple Class class Point definitialize(x, y) @x = x @y = y end defx @x end defx=(value) @x = value end end p = Point.new(3,4) puts "p.x is #{p.x}" p.x = 44 CS 142 Lecture Notes: Ruby

22. Metaprogramming • Programs that write programs! • eval, instance_eval, class_eval class Automobile include Extendable End a = Automobile.new a.add_variable :color a.add_variable :brand a.color = "green" a.brand = "Mazda" puts a.color, a.brand Mixin that gives the add_variablemethod These method invocations add accessor functions CS 142 Lecture Notes: Ruby

23. CS 142 Lecture Notes: Ruby