The Enumerable Module or How I Fell in Love with Ruby

Presented at Cascadia Ruby Conf 2011 July 29, 2011 in Seattle, WA by Haris Amin. The presentation can be viewed here http://confreaks.net/videos/607-cascadiaruby2011-the-enumerable-module-or-how-i-fell-in-love-with-ruby

Transcript

1. THE ENUMERABLE MODULE or How I Fell In Love with Ruby! Haris Amin Cascadia Ruby Conf 2011 07/29/2011 Monday, August 1, 2011
2. WHO IS THIS GUY? • Haris Amin • Software/Web Developer • Live in New York City Monday, August 1, 2011
3. THESE GUYS MAKE SURE I’M NOT LIVING IN THE STREETS Monday, August 1, 2011
4. WHAT WE DO @ ? Shoulder Pressing Colleagues Healthy Programmer Vertebrates Monday, August 1, 2011
5. LOOK MA I HAS DEGREE! • Studies Physics/Math in Undergrad • E = mc^2 , doesn’t pay for food • Programming, for me in college was just a means to compute something Monday, August 1, 2011
6. LAST TALK I GAVE AT A CONFERENCE? • Simulation of Viscoelastic Fluids • What did I do? • Employed a weighted-norm least-squares finite element method to approximate the solution to Oldroyd-B equations • So...yeah... for me programming was just a way to compute stuff :) Monday, August 1, 2011
7. THOUGHT TO MYSELF... Arrays & Hashes ARE FUN!!!! Monday, August 1, 2011
8. WHAT IS THE ENUMERABLE MODULE? • A module, you can MIX IT IN! • A bunch of methods that work with collections • Empowers the most notably the Array and Hash classes (among others i.e. Set, Range, File, etc.) Monday, August 1, 2011
9. HOW TO ‘MIX-IN’ THE ENUMERABLE? • A class ‘including’ or ‘mixing-in’ Enumerable must define the ‘#each’ method • Yielded items from the #each method empower the collection awareness for the class Monday, August 1, 2011
10. • The #collect method executes the provided block to all of the values yielded by #each class PlanetExpress include Enumerable def each yield “Bender” yield “Frye” yield “Leela” yield “Zoidberg” end end PlanetExpress.new.collect do |member| “#{member} works at Planet Express” end Monday, August 1, 2011
11. BUT WHY IS ENUMERABLE SO... SEXY!? ... ... ... Monday, August 1, 2011
12. LOOK AT ALL THESE METHODS! •all?, any?, collect, detect, each_cons, each_slice, each_with_index, entries, enum_cons, enum_slice, enum_with_index, find, find_all, grep, include?, inject, map, max, member?, min, partition, reject, select, sort, sort_by, to_a, to_set, zip Monday, August 1, 2011
13. PROGRAMMER HAPPINESS “Programmers often feel joy when they can concentrate on the creative side of programming, so Ruby is designed to make programmers happy.” - Yukihiro Matsumoto (Matz) Monday, August 1, 2011
14. WATCH OUT FOR DR. ZOIDBERG’S TIPS Monday, August 1, 2011
15. LET’S TAKE A LOOK AT SOME ENUMERABLE METHODS... Monday, August 1, 2011
16. each • The #each method yields items to a supplied block of code one at a time • Classes implement #each differently names = %w{ Frye Leela Zoidberg } names.each do |name| “#{name} works at Planet Express” end Monday, August 1, 2011
17. find • Elegantly simple, find one item that matches the condition supplied by the block • Consider how a library like ActiveRecord would reimplemnt find from Enumerable? names = %w{ Frye Leela Zoidberg } names.find { |name| name.length > 4} Monday, August 1, 2011
18. group_by • It takes a block, and returns a hash, with the returned value from the block set as the key • Consider how one could use this as word count for a document/text names = %w{ Frye Bender Leela Zoidberg } names.group_by { |name| name.length} # => {4=>["Frye"], 6=>["Bender"], 5=>["Leela"], 8=>["Zoidberg"]} Monday, August 1, 2011
19. grep • Searches for members of the collection according to a pattern.... pattern matching • It uses the === operator for pattern matching names = %w{ Frye Bender Leela Zoidberg } names.grep(/oidber/) # => ["Zoidberg"] Monday, August 1, 2011
20. GREP-ALICOUS! • Using the === allows us to do some fancy matching • We can grep for types or objects • Equivalent to stuff.select { |element| String === element} Dr. Zoidberg’s Tip (The doctor is in!) stuff = [ “Zoidberg”, Pizza.new, :homeless, “Dr."] stuff.grep(String) # => [ “Zoidberg”, “Dr.”] Monday, August 1, 2011
21. map / collection • Think of it as a transformation method, that applies the block as a transformation • Always returns a new Array with the transformation applied • Different then #each, return value matters with #map names = %w{ Frye Bender Leela Zoidberg } names.map { |name| name.downcase } # => [“frye”, “bender”, “leela”, “zoidberg” ] Monday, August 1, 2011
22. THE DELICIOUS ENUMERATOR ... enum ... enum ... enum Monday, August 1, 2011
23. ENUMERATOR • We can create an Enumerator without mixing-in the Enumerable module and still have the power of Enumerable methods • 3 ways to create Enumerator without mixing-in Enumerable 1. Create Enumerator explicitly with a code block 2. Attach an Enumerator to another object 3. Create Enumerator implicitly with blockless iterators Monday, August 1, 2011
24. Create Enumerator explicitly with a code block • y is the yielder, an instance of Enumerator::Yielder • You don’t yield from the block, you only append to the yielder e = Enumerator.new do |y| y << “Frye” y << “Bender” y << “Leela” y << “Zoidberg” end Monday, August 1, 2011
25. Attach an Enumerator to another object • knows/learns how to implement #each from another object • we’re binding the Enumerator to the #select method of the names array names = %w { Frye Bender Leela Zoidberg } e = names.enum_for(:select) Monday, August 1, 2011
26. Create Enumerator implicitly with blockless iterators • most iterators when called without a block return an Enumerator • our blockless iterator returned the same Enumerator as the enum_for approach names = %w { Frye Leela Bender } names.enum_for(:select) # => #<Enumerator: ["Frye", "Leela", "Bender"]:map> names.map # => #<Enumerator: ["Frye", "Leela", "Bender"]:map> Monday, August 1, 2011
27. BUT WHY DO WE CARE? ...USES? Monday, August 1, 2011
28. Add Enumerability to an existing object • Now we can use Enumerable methods on our ship object module PlanetExpress class Ship PARTS= %w{ sprockets black-matter } def survey_parts PARTS.each {|part| yield part } end end end ship = PlanetExpress::Ship.new enum = ship.enum_for(:survey_parts) Monday, August 1, 2011
29. Fine Grained Iteration • An Enumerator is an object, it can maintain state • Think film reels, state machines, etc... scenes = %w{ credits opening climax end } e = scenes puts e.next puts e.next e.rewind puts e.next Monday, August 1, 2011
30. CHAINING ENUMERATORS... ...HMMM Monday, August 1, 2011
31. CHAINING ENUMERATORS • Normally chaining enumerators isn’t very useful • names.map.select might as well be names.select • Most enumerators are just passing the array of values down the chain Monday, August 1, 2011
32. LAZY SLICE • Instead of creating a 2-element slices for the whole array in memory, the enumerator can create slices in a “lazy” manner and only create them as they are needed Dr. Zoidberg’s Tip (can i have a slice) names = %w { Frye Bender Leela Zoidberg } names.each_slice(2).map do |first, second| “#{first} gets a slice & #{second} gets a slice” end Monday, August 1, 2011
33. MAP WITH INDEX...WTF? • There is no #map_with_index defined in Enumerable • Ah but we can chain... chain... chain! Dr. Zoidberg’s Tip (what map? i don’t even know where we are!) names = %w { Leela Bender Frye Zoidberg } names.map.with_index do |name, i| “#{name} has a rank #{i}” end Monday, August 1, 2011
34. THE SET CLASS Monday, August 1, 2011
35. WHAT IS SET? • The Set class is a Standard Lib class in Ruby • You use it by requiring it explicitly ( require ‘set’ ) • It stores a collection of unordered, unique values • It mixes-in the Enumerable module Monday, August 1, 2011
36. SET IS ENUMERABLE class Set include Enumerable #... def each block_given? or return enum_for(__method__) @hash.each_key { |o| yield(o) } self end end • Calls a block for each member of the set passing the member as a parameter • Returns an enumerator if no block is given Monday, August 1, 2011
37. SET IS ENUMERABLE • Actually uses Hash for implementing unique values class Set include Enumerable #... def initialize @hash ||= Hash.new enum.nil? and return if block do_with_enum(enum) { |o| add(block[o]) } else merge(enum) end end end Monday, August 1, 2011
38. SET IS ENUMERABLE • Defines its own implementation of Enumerable methods class Set include Enumerable #... def include? @hash.include?(o) end alias member? include? end Monday, August 1, 2011
39. ARE YOU IN LOVE YET? Monday, August 1, 2011
40. THEN READ THIS • This talk was inspired by the AWESOME discussion of Enumerable by David A. Black • READ IT! SPREAD THE WORD!!!! Monday, August 1, 2011
41. THANK YOU! hamin harisamin harisamin.tumblr.com Monday, August 1, 2011