Introduction to information systems RUBY dr inż. Tomasz Pieciukiewicz

Agenda  Ruby –general information  Syntax and semantics

Ruby  interpreted, dynamically typed programming language  created in 1995 by Yukihiro Matsumoto  became popular thanks to Ruby on Rails framework

Comments  Comments start with #  „broken” lines have to end with \ :puts\ "brokenline"  Commands don’t have to end with semicolon (or any other character)

Numbers  No limits on number size  _ may be used to separate groups of three digits from each other to increase readability: 12_345_678_901  Real numbers – „traditional” or expotential format: e-4

Strings  Strings – in " or ' puts "string in quotes" puts 'string in apostrophes'  Or using "%q syntax" puts %q!string! puts %Q{string} puts %

Strings  Multiline strings use <<TOKEN syntax print <<HERE I am a multiline string HERE

Variables  A variable is defined by value assignment text= "I am a string"  Variable names start with _ or a..z (but there are exceptions), may contain small and capital letters, digits and _.  Multi-word variable names use CamelCase: VariableNameInCamelCase

Expression interpolation  Interpolation of variables in quoted strings: "My name is #{name}"  Any expression may be put in #{…}

Symbols  Symbols are an equivalent for enumeration – after a fashion. Name of a symbol with colon in front: :ISP_address

Constants (sort of)  Constants names are written in caps: PI = 3.141_592_653  Their values may be redefined during program execution (but we'll get a warning ;) )

Arrays  Arrays are used and created like in other languages: array= [1,2,3,"I am", "an array"] puts array[0] array[0]=4  Negative array index – starting at the end of the table, counting backwards: puts array[-1]

Arrays  Processing multiple array elements – provide two values for index, first is the starting point, second– number of elements to be processed: array[3,2]="aaa"

Maps  Tables indexed using numbers, and/or strings or symbols: Map=/ {"Key"=>40,"Another"=>"value"} puts AsocArray["Key"]

Ranges  Range is defined using.. and … operators range= 1…4 #1,2,3 range= 1..4 #1,2,3,4 range= "a".."z"  Few useful methods:  to_a – convert range to an array  min – first element  max – last element

If if(cnd1) … elsif(cnd2) … else … end … if (cnd)

Unless unless(cnd) … else … end … unless (cnd)

Case case expression when v1 … when v2 … else … end

While and Until loops while(cnd) … end until(cnd) … end

Iterators  upto and downto – for equivalent, step 1 or -1: startingValue.upto(endValue) do |variable| … end 0.upto(array.length-1) do |loop_index| … end

Iterators  step – for with step different than 1 startValue.step(endValue, step) do \ |variable| … end 4.step(12,2) do |i| … end

Iterators  times – loop executed a specific number of times: howMany.times do … end 5.times do … end

Iterators  each–foreach once again collection.each do |variable| … end

Loops and iterators  Keywords that may be used in loops and iterators:  break – ends the loop  redo – redo the current iteration  next – move on to next iteration  retry – re-start the loop

Methods  method definition: def name(paramsList) … end def join (FirstWord, SecondWord) return FirstWord+" "+SecondWord end

Methods  Variable number of parameters –last defined argument preceded with * def join(FirstWord, *others) return FirstWord+" "+others.join(" ") end  Last parameter is treated like a table! If a table is to be passed as a parameter, its name should be preceded with *

Methods  Returning multiple values –separate values with commas, method returns an array: def RetArray return 1,2,3 end

Blocks  Section of code that may be passed to a method like a parameter  Blocks are enclosed in curly brackets or between do and end keywords  Blocks are invoked with the yield keyword

Blocks def greeting() yield end greeting {puts"Hello"}

Blocks  Blocks may be parametrized def greeting() yield "Hello" end greeting {|param| puts param}

BEGIN and END blocks  Code put in block marked as BEGIN is executed automatically after a program is loaded  Code put in block marked as END is executed automatically after a program finishes execution

Classes  Simplest class definition: class Name end  Class names ALWAYS start with a capital letter

Classes  initialize method–constructor class Name def initialize(parameters) … end

Classes  Instance and class attributes: – instance attributes  – class attributes  Attributes are usually initialized by the initialize method. Like variables –they are created by value assignment!

Classes  Object creation – using the new method, which invokes initialize()  instance= Name.new(parameters)

Classes  Getters/setters class Animal def color() end def color=(color) end

Classes  Auto-generated getters and setters: class Animal attr_reader:color attr_writer:color end  or class Animal attr_accessor:color end

Classes  Inheritance – operator < classDog < Animal … end  If necessary (usually), superclass constructor is invoked with super(parameters)

Classes  Access levels:  public  protected  private  Modifiers are used somewhere in the  class body, everything declared after  modifier has the new access level

Classes  class methods are defined by preceding the method name with class name: class Name def Name.method(parameters) … end

Modules  May be used to group classes and "independent" methods defined using the module keyword: module ModuleName  Imported using  include 'module.extension'  require 'module' (file extension has to be.rb)

Modules  Can't create module instances, so "independent" methods are usually class(or rather module) methods  Classes defined within module (like internal classes) are accessed with ModuleName::ClassName

Modules  Non-class independent methods may be imported into a class with include ModuleName  methods from many modules may be imported into a single class all will be treated as if they were defined within the class

Recommended Reading

 Programming Ruby 1.9 & 2.0 (4th edition): The Pragmatic Programmers' Guide, Dave Thomas, Chad Fowler, Andy Hunt  Metaprogramming Ruby 2: Program Like the Ruby Pros, Paolo Perrotta  Eloquent Ruby, Russ Olsen, Addison-Wesley 2011

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