Lecture 1. Basic Ruby 1 / 61

Transcription

1 Lecture 1 Basic Ruby 1 / 61

2 What does this do? 3.times do print 'Hello, world!' end 2 / 61

3 Why Ruby? Optimized for programmer happiness Used for Ruby on Rails Very popular web framework 3 / 61

4 Course Policies 4 / 61

5 Prerequisites CIS 120 (or instructor permission) Basic HTML/CSS knowledge Codecademy Mozilla Developer Network W3Schools Please speak with us if you do not have the prerequisites or have any other concerns 5 / 61

6 CIS 19x Course Structure 3 shared lectures during semester 8/28: Git 9/11: Command Line 9/18: How the Web works Learn about language in "recitation" sections 6 / 61

7 CIS 196 Course Structure Lecture Topics: 3 weeks on Ruby programming language 6 weeks on Ruby on Rails web framework 5 weeks on miscellaneous topics 9 homework assignments 1 final project For more details, read the course syllabus 7 / 61

8 Grading 70% - Homework 25% - Final Project 5% - In-class Participation 8 / 61

9 Homework Due on Thursdays at 11:59pm through GitHub Classroom Unlimited submissions Your latest submission will be used for grading One free late day to use on any assignment After, 20% will be deducted for each day late 9 / 61

10 Homework Grading Correctness (15 pts) Style (5 pts) Best Practices (5 pts) Full credit if you pass all tests on Travis CI (unless told otherwise) Full credit if you have no Rubocop offenses TAs will manually grade your code to ensure the Ruby Way 10 / 61

11 Final Project Must be a web app built using Ruby on Rails Must be approved by Desmond/Sanjana ahead of time Milestones to help keep you on track Will be "due" the last day of class Demo on one of the Reading Days at the Project Fair 11 / 61

12 In-class Participation Attending and participating in lectures will be very beneficial for you To help encourage you to come to class, we will use Poll Everywhere during class Polls will be scattered throughout lecture You will receive participation grade based on: Completing polls while in class 12 / 61

13 Poll Everywhere Get started by going to When asked to provide a screen name, make it your preferred first name combined with your last name Otherwise you won't get points for participating 13 / 61

14 Which site uses Ruby on Rails? GitHub Piazza Canvas Airbnb All of the above! Poll 14 / 61

15 Why are you taking this class? Poll 15 / 61

16 Academic Integrity Don't copy/paste others' code Don't have mid-level discussions High-Level Discussion What is Rails used for? Mid-Level Discussion How did you do Homework 1? Low-Level Discussion What is the syntax for iterators? 16 / 61

17 O ce Hours Weekday Time TA Thursday 5-7pm Desmond Tuesday 7-9pm Sanjana Wednesday 5-7pm Zena Tuesday 6-8pm Edward TBD TBD Zhilei All office hours will be held in Moore / 61

18 Course Websites CIS 196 Website - All relevant course info Piazza - All course discussions & communication GitHub - Homework assignment management Travis CI - Results of tests run on submission Note that we will be using travis-ci.com Canvas - Viewing grades 18 / 61

19 Ruby 19 / 61

20 What you'll need Text editor (Sublime Text is probably easiest) Command Line If you use Windows, you must use a Linux VM or dual boot Linux Ruby We have provided a VM here with Ruby and Rails pre-installed If you run Ruby on Windows, I nor your TAs will debug for you 20 / 61

21 Installing Ruby Use the Ruby Version Manager (RVM) to manage and install Ruby versions Use this even if you plan on just using one version In this class, we will be using version Make sure you download the correct version 21 / 61

22 Resources Use the Ruby Docs whenever you get stuck Make sure you're looking at the correct version (2.5.1) This class will follow this style guide 10 points of your homework grade come from style and best practices 5 of which come from Rubocop (more on this later) 22 / 61

23 History of Ruby Ruby was designed in the mid-90s by Yukihiro "Matz" Matsumoto Influenced by Perl, Smalltalk, Eiffel, Ada & Lisp (Matz's favorite languages) Achieved mass acceptance in 2006 Much of Ruby's success and growth can be attributed to Rails Read about Matz's inspiration for Ruby here 23 / 61

24 Running Ruby Use a REPL (Read-Execute-Print-Loop) with the irb command in terminal Allows you to write and execute Ruby code from the Command Line This is great for testing Get out of the REPL by entering quit Execute.rb files with the ruby command: ruby file.rb 24 / 61

25 Types in Ruby Almost everything in Ruby is an object Ruby is strongly typed Every object has a fixed type Ruby is dynamically typed Variables do not need to be initialized Compare to Java which is statically typed 25 / 61

26 Will this give me an error? int_var = 5 int_var = 'five' Poll 26 / 61

27 Printing in Ruby You can print a value with three different commands: print, puts, and p print outputs the value and returns nil puts outputs the value with a newline and returns nil p both outputs and returns the value I'll use p in my examples since it formats output better I will denote output with #=> p 'hello world' #=> "hello world" 27 / 61

28 Numerics There are several types of numbers in Ruby Unlike Java, numbers are also objects in Ruby The main ones you'll be using are instances of the Integer and Float classes This is helpful to know when looking at the Ruby Docs If you see anything about FixNum or BigNum, note that they were deprecated in Ruby / 61

29 Local Variables Since Ruby is dynamically typed, you don't need to declare types (like int, String, etc.) Local variables are assigned to bare words foo = 100 p foo #=> / 61

30 Strings Strings can be denoted with either single or double quotes They can be concatenated together with + and appended with << hello = 'Hello' world = 'world!' foo = hello + ', ' + world p foo #=> "Hello, world!" p hello #=> "Hello" hello << '!' p hello #=> "Hello!" Note that concatenation did not change the variable, but appending did 30 / 61

31 Escaped Characters only work in Double Quotes print 'hello\nworld' #=> hello\nworld print "hello\nworld" #=> hello world 31 / 61

32 Only Double Quotes support String Interpolation When inserting variables into strings, string interpolation is preferred Put local variable betwen the curly braces in #{} This calls to_s on the variable foo = 5 p "Hello, #{foo}!" #=> "Hello, 5!" # Compare to: p 'Hello, ' + foo.to_s + '!' #=> "Hello, 5!" 32 / 61

33 When to use Single Quotes vs. Double Quotes Use double quotes if: You're using escaped characters or string interpolation You want to include single quotes in the string In all other cases, use single quotes It makes for more readable code 33 / 61

34 Which has the best Ruby style? Poll '5 + 5 = ' + (5 + 5).to_s "5 + 5 = 10" "5 + 5 = #{5 + 5}" 34 / 61

35 Symbols Denoted with a colon in front They are immutable For example, you cannot do :a << :b because that would change :a They are unique The equal? method checks if the two objects are the same 'hi'.equal? 'hi' #=> false :hi.equal? :hi #=> true 35 / 61

36 Boolean States All Ruby objects have boolean states of either true or false In fact, the only two objects in Ruby that are false are nil and false itself All other objects are true nil is an object that represents nothingness Kind of like Java's null 36 / 61

37 If Statements Conditionals can be used for control flow and to return different values based on the condition They implicitly return the last evaluated expression Use the elsif keyword for more branching foo = if true 1 elsif false 2 else 3 end p foo #=> 1 37 / 61

38 Unless Statements Evaluated when the condition is false Equivalent to if not Note that you should never have an unless statement followed by an else Instead, use an if... else flow unless false p 'hello' end #=> "hello" 38 / 61

39 Conditional Modi ers if and unless can be placed at the end of the line This helps code read more like English These are prefered for one liners p 'hello' if true #=> "hello" p 'bye' unless false #=> "bye" 39 / 61

40 Ternary Operator When using one line if-else statements, favor the ternary operator p true? 'hello' : 'goodbye' #=> "hello" p false? 'hello' : 'goodbye' #=> "goodbye" 40 / 61

41 Which of these has the best Ruby style? p 'hello' if not 'Desmond'.nil? p 'hello' unless 'Desmond'.nil? p 'Desmond'? ('Sanjana'? 'hello' : 'goodbye') : 'hi' p 'hello' if 'Desmond' Poll 41 / 61

42 Methods Parentheses around arguments can be omitted if unambiguous Our Style Guide has a lot to say about methods & parentheses def hi 'hello, there' end def hello(name) puts "hello, #{name}" end puts hi #=> "hello, there" hello('matz') #=> "hello, Matz" hello 'DHH' #=> "hello, DHH" 42 / 61

43 Implicit Returns Methods in Ruby always return exactly one thing They will return the last executed expression This means that you do not have to explicitly type return x at the end of the method Only use the return keyword when you want to exit a method early 43 / 61

44 Method Names While not strictly enforced, Ruby has certain conventions with naming methods If a method ends in:?, it should return a boolean (e.g. Array#empty?) =, it should write to a variable (e.g. writer methods)!, it should potentially change the variable being called on or perform some other dangerous action (e.g. String#capitalize!) You will encounter each kind as the course progresses 44 / 61

45 Default Arguments Denoted with an equal sign and value in method signature Optional when calling method def hello(name = 'world') p "Hello, #{name}" end hello #=> "Hello, world" hello('matz') #=> "Hello, Matz" 45 / 61

46 Guard Clauses Instead of wrapping an entire method in a conditional, use a guard clause to exit early # bad def foo(bar) if bar p 'hello' p 'goodbye' end end # good def foo(bar) return unless bar p 'hello' p 'goodbye' end 46 / 61

47 What's wrong with this method? def hello(name) return unless name puts "Hello #{name}" puts 'Goodbye' if not name.empty? end Poll It uses parentheses in the method definition It uses the return keyword It uses string interpolation instead of concatenation It uses if not Nothing! 47 / 61

48 Arrays Instantiated with [] or Array.new, but [] is preferred Note that you don't have to specify a size Arrays are heterogeneous Elements can be of different types The shovel operator << is the preferred way to add elements to the end of an array a = [] a << 1 p a #=> [1] 48 / 61

49 Iterators There are for... in loops in Ruby, but they are discouraged You will never have to use one in this class The Ruby Way is to use iterators The most basic one is the each iterator foo = [1, 2, 3] foo.each do num print "#{num} " end #=> "1 2 3 " 49 / 61

50 Blocks This is the code between the do and end keywords It is convention to use the do... end keywords when the block spans multiple lines But they should be replaced by { } when the method is only one line long Or a method is being chained off of the block [1, 2, 3].each { n print "#{n} " } #=> "1 2 3 " p [1, 2, 3].map { n n + 1 }.join(' ') #=> "2 3 4" 50 / 61

51 Hashes Used to store key-value pairs Like maps in Java Instantiated with {} and Hash.new but {} is preferred Keys can be ANY object They're often symbols Values can be accessed with [] foo = {} foo[:hello] = 'world' p foo #=> {:hello=>"world"} p foo[:hello] #=> "world" 51 / 61

52 Alternate Hash Syntax => is called a hash rocket It is the default notation linking key and value Starting with Ruby 2.0, an alternate syntax can be used Only when the key is a symbol This syntax is preferred if all keys are symbols foo = { foo: 'bar', baz: 'foobar' } p foo #=> {:foo=>"bar", :baz=>"foobar"} 52 / 61

53 Managing Dependencies 53 / 61

54 Gems Ruby libraries are called gems The command to install them is gem install gem_name When installed, the gem is installed in the current Ruby version's gem directory To use a gem, pass the name of the gem as a string to the require method at the top of the file (e.g. require pry) 54 / 61

55 The Bundler Gem Bundler is used to manage dependencies, comes in handy in large projects Install the gem using gem install bundler To use, create Gemfile in the directory & add gems to it Run bundle install or bundle for short to install all gems in the Gemfile 55 / 61

56 The Pry Gem A very useful gem for debugging gem install pry and add require pry to the top of the file Insert the line binding.pry in a Ruby file When you run the program, Ruby will stop at that line and give you a REPL with all variables in scope binding.pry must be deleted from your homework assignments before submitting because it will cause your tests to fail 56 / 61

57 The Rubocop Gem Rubocop will be used to grade for Style To run Rubocop: 1. Install Rubocop by running gem install rubocop 2. Make sure that you're in the directory that you want to check 3. Run rubocop 57 / 61

58 The RSpec Gem RSpec will be used for testing Be sure to run gem install rspec You will learn more about RSpec and writing tests in 2 lectures For now, you will be able to run pre-written tests by running rspec from the Command Line 58 / 61

59 Homework 1 59 / 61

60 Homework 1 Released now, due next Thursday at 11:59pm When you get started, you'll want to run gem install bundler and bundle install You can run rspec at any time during development to see how you're doing against the test cases You can run rubocop at any time to see how you're doing on style This means that you don't have to submit every time you want to see your output 60 / 61

61 Homework 1 You will: Set up everything you need to get started with Ruby Complete 5 methods designed to get you more comfortable with Ruby Submit to GitHub Classroom & view results on Travis CI You will fill out exercises.rb There is a provided file called bin/console.rb that will execute your code You can run ruby bin/console.rb and call all of the methods that you defined in exercises.rb 61 / 61