The Enumerable Module or How I Fell in Love with Ruby

THE ENUMERABLE MODULE or How I Fell In Love with Ruby! Haris Amin Cascadia Ruby Conf 2011 07/29/2011Monday, August 1, 2011

WHO IS THIS GUY? • Haris Amin • Software/Web Developer • Live in New York CityMonday, August 1, 2011

THESE GUYS MAKE SURE I’M NOT LIVING IN THE STREETSMonday, August 1, 2011

WHAT WE DO @ ? Shoulder Pressing Colleagues Healthy Programmer VertebratesMonday, August 1, 2011

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 somethingMonday, August 1, 2011

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

THOUGHT TO MYSELF... Arrays & Hashes ARE FUN!!!!Monday, August 1, 2011

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

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 classMonday, August 1, 2011

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 • The #collect method executes the provided block to all of the values yielded by #eachMonday, August 1, 2011

BUT WHY IS ENUMERABLE SO... ... ... ... SEXY!?Monday, August 1, 2011

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, zipMonday, August 1, 2011

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

WATCH OUT FOR DR. ZOIDBERG’S TIPSMonday, August 1, 2011

LET’S TAKE A LOOK AT SOME ENUMERABLE METHODS...Monday, August 1, 2011

each names = %w{ Frye Leela Zoidberg } names.each do |name| “#{name} works at Planet Express” end • The #each method yields items to a supplied block of code one at a time • Classes implement #each differentlyMonday, August 1, 2011

find names = %w{ Frye Leela Zoidberg } names.find { |name| name.length > 4} • Elegantly simple, ﬁnd one item that matches the condition supplied by the block • Consider how a library like ActiveRecord would reimplemnt ﬁnd from Enumerable?Monday, August 1, 2011

group_by names = %w{ Frye Bender Leela Zoidberg } names.group_by { |name| name.length} # => {4=>["Frye"], 6=>["Bender"], 5=>["Leela"], 8=>["Zoidberg"]} • 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/textMonday, August 1, 2011

grep names = %w{ Frye Bender Leela Zoidberg } names.grep(/oidber/) # => ["Zoidberg"] • Searches for members of the collection according to a pattern.... pattern matching • It uses the === operator for pattern matchingMonday, August 1, 2011

GREP-ALICOUS! stuff = [ “Zoidberg”, Pizza.new, :homeless, “Dr."] stuff.grep(String) # => [ “Zoidberg”, “Dr.”] • 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!)Monday, August 1, 2011

map / collection names = %w{ Frye Bender Leela Zoidberg } names.map { |name| name.downcase } # => [“frye”, “bender”, “leela”, “zoidberg” ] • 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 #mapMonday, August 1, 2011

THE DELICIOUS ENUMERATOR ... enum ... enum ... enumMonday, August 1, 2011

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 iteratorsMonday, August 1, 2011

Create Enumerator explicitly with a code block e = Enumerator.new do |y| y << “Frye” y << “Bender” y << “Leela” y << “Zoidberg” end •y is the yielder, an instance of Enumerator::Yielder • You don’t yield from the block, you only append to the yielderMonday, August 1, 2011

Attach an Enumerator to another object names = %w { Frye Bender Leela Zoidberg } e = names.enum_for(:select) • knows/learns how to implement #each from another object • we’re binding the Enumerator to the #select method of the names arrayMonday, August 1, 2011

Create Enumerator implicitly with blockless iterators names = %w { Frye Leela Bender } names.enum_for(:select) # => #<Enumerator: ["Frye", "Leela", "Bender"]:map> names.map # => #<Enumerator: ["Frye", "Leela", "Bender"]:map> • most iterators when called without a block return an Enumerator • our blockless iterator returned the same Enumerator as the enum_for approachMonday, August 1, 2011

BUT WHY DO WE CARE? ...USES?Monday, August 1, 2011

Add Enumerability to an existing 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) • Now we can use Enumerable methods on our ship objectMonday, August 1, 2011

Fine Grained Iteration scenes = %w{ credits opening climax end } e = scenes puts e.next puts e.next e.rewind puts e.next • An Enumerator is an object, it can maintain state • Think ﬁlm reels, state machines, etc...Monday, August 1, 2011

CHAINING ENUMERATORS... ...HMMMMonday, August 1, 2011

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 chainMonday, August 1, 2011

LAZY SLICE names = %w { Frye Bender Leela Zoidberg } names.each_slice(2).map do |first, second| “#{first} gets a slice & #{second} gets a slice” end • 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)Monday, August 1, 2011

MAP WITH INDEX...WTF? names = %w { Leela Bender Frye Zoidberg } names.map.with_index do |name, i| “#{name} has a rank #{i}” end • 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!)Monday, August 1, 2011

THE SET CLASSMonday, August 1, 2011

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 moduleMonday, August 1, 2011

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 givenMonday, August 1, 2011

SET IS ENUMERABLE 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 • Actually uses Hash for implementing unique valuesMonday, August 1, 2011

SET IS ENUMERABLE class Set include Enumerable #... def include? @hash.include?(o) end alias member? include? end • Deﬁnes its own implementation of Enumerable methodsMonday, August 1, 2011

ARE YOU IN LOVE YET?Monday, August 1, 2011

THEN READ THIS • Thistalk was inspired by the AWESOME discussion of Enumerable by David A. Black • READ IT! SPREAD THE WORD!!!!Monday, August 1, 2011

THANK YOU! hamin harisamin harisamin.tumblr.comMonday, August 1, 2011

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The Enumerable Module or How I Fell in Love with Ruby

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The Enumerable Module or How I Fell in Love with Ruby — Presentation Transcript