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RUBYCONF 2020 Ariel Caplan • @amcaplan • amcaplan.ninja The Humble Hash

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LIFE

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cell.next_state = if cell.alive? [2,3].include?(cell.live_neighbors_count) ? 1 : 0 else cell.live_neighbors_count == 3 ? 1 : 0 end

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RUBYCONF 2020 • ARIEL CAPLAN • @AMCAPLAN •

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RUBYCONF 2020 • ARIEL CAPLAN • @AMCAPLAN • • Ruby programmer since 2014 • Backend Developer at • Find me online: @amcaplan • https://amcaplan.ninja Hi! I’m Ariel Caplan.

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RUBYCONF 2020 • ARIEL CAPLAN • @AMCAPLAN • talk[:basics]

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RUBYCONF 2020 • ARIEL CAPLAN • @AMCAPLAN • • Performant key-value pair store • Keys and values can be any Ruby object • Literal syntax: • Explicit syntax: • Strict fetching: • Fetching with default value: • Setting a different default value: What is a Hash? { key: "value" } hash = Hash.new hash[:key] = "value" hash[:key] #=> "value" hash[:non_key] #=> nil hash.fetch(:key) hash = Hash.new(4) hash[:non_key] #=> 4

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RUBYCONF 2020 • ARIEL CAPLAN • @AMCAPLAN • talk[:obj_key][:set]

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RUBYCONF 2020 • ARIEL CAPLAN • @AMCAPLAN • Set require 'set' set = Set.new([1,2,3]) #=> # set.include?(3) #=> true set.include?(4) #=> false set.add(4) #=> # set.add(3) #=> #

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def add(o) @hash[o] = true self end def merge # ... do_with_enum(enum) { |o| add(o) } # ... end class Set def initialize(enum = nil, &block) @hash ||= Hash.new(false) # some other stuff merge(enum) end RUBYCONF 2020 • ARIEL CAPLAN • @AMCAPLAN • Set def include?(o) @hash[o] end end

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RUBYCONF 2020 • ARIEL CAPLAN • @AMCAPLAN • talk[:obj_key][:cache]

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RUBYCONF 2020 • ARIEL CAPLAN • @AMCAPLAN • Disclaimers # disclaimer { key: "network", value: "tier_a", text: "To receive the lowest out-of-pocket costs, please choose a provider in the Tier A network." } # provider metadata { specialty: "periodontist", network: "tier_a" }

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RUBYCONF 2020 • ARIEL CAPLAN • @AMCAPLAN • Disclaimers # 500 x 300 = 150,000 operations # once per disclaimer - 300 disclaimers disclaimers.select { |disclaimer| # once per provider - 500 providers providers.any? { |provider| provider.metadata[disclaimer[:key]] == disclaimer[:value] } }.map { |disclaimer| disclaimer[:text] }

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RUBYCONF 2020 • ARIEL CAPLAN • @AMCAPLAN • Disclaimers # 500 + 300 = 800 operations # once per provider - 500 providers provider_data = Set.new providers.each do |provider| provider.metadata.each do |key, value| provider_data << { key: key, value: value } end end # once per disclaimer - 300 disclaimers disclaimers.select { |disclaimer| data = { key: disclaimer[:key], value: disclaimer[:value] } provider_data.include?(data) }.map { |disclaimer| disclaimer[:text] }

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RUBYCONF 2020 • ARIEL CAPLAN • @AMCAPLAN • ! • String • Symbol • Numeric • !1.0.eql?(1) • Array • Hash " • Anything for which equality isn’t obvious Hash Key Warning! Containing valid types {

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RUBYCONF 2020 • ARIEL CAPLAN • @AMCAPLAN • talk[:defaults][:wizardry]

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RUBYCONF 2020 • ARIEL CAPLAN • @AMCAPLAN • • 1 object that will always be returned • Doesn’t set a key-value pair • Set at hash initialization: • Set after hash initialization Defaults Deep Dive: Default Value Hash.new(4) hash = {} hash.default = 4

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RUBYCONF 2020 • ARIEL CAPLAN • @AMCAPLAN • • Gotcha: It will always be the same object! Defaults Deep Dive: Default Value hash = Hash.new("abc") str = hash[:key] str << "d" hash[:another_key] #=> "abcd"

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RUBYCONF 2020 • ARIEL CAPLAN • @AMCAPLAN • • Proc that will be run when a key is not found • Can set a key-value pair, if you want • Set at hash initialization: • Set after hash initialization Defaults Deep Dive: Default Proc hash = Hash.new { |h, k| h[k] = 4 } hash = {} hash.default_proc = ->(h, k) { h[k] = 4 }

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RUBYCONF 2020 • ARIEL CAPLAN • @AMCAPLAN • Default Proc Can Reference Itself! default_proc = ->(h, k) { h[k] = Hash.new(&default_proc) } hash = Hash.new(&default_proc) hash[:a][:b][:c] = 4 hash #=> {:a=>{:b=>{:c=>4}}}

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RUBYCONF 2020 • ARIEL CAPLAN • @AMCAPLAN • Fibonacci Sequence Fn = Fn-2 + Fn-1 0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55…

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RUBYCONF 2020 • ARIEL CAPLAN • @AMCAPLAN • Fibonacci Sequence: Iterative def fib(n) i, j = 0, 1 counter = 0 while counter < n i, j = j, i + j counter += 1 end i end

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RUBYCONF 2020 • ARIEL CAPLAN • @AMCAPLAN • Fibonacci Sequence: Recursive def fib(n) case n when 0, 1 n else fib(n - 2) + fib(n - 1) end end

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RUBYCONF 2020 • ARIEL CAPLAN • @AMCAPLAN • Fibonacci Sequence: Default Proc hash = Hash.new { |h, k| h[k] = h[k-2] + h[k-1] } hash[0] = 0 hash[1] = 1

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RUBYCONF 2020 • ARIEL CAPLAN • @AMCAPLAN • Fibonacci Performance fib(4) fib(2) fib(1) fib(0) fib(3) fib(2) fib(1) fib(1) fib(0)

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RUBYCONF 2020 • ARIEL CAPLAN • @AMCAPLAN • Fibonacci Performance hash[4] hash[2] hash[1] hash[0] hash[1] hash[3] hash[2]

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RUBYCONF 2020 • ARIEL CAPLAN • @AMCAPLAN • Fibonacci Performance hash[4] hash[2] hash[1] hash[0] hash[1] hash[3] hash[2] fib(4) fib(2) fib(1) fib(0) fib(3) fib(2) fib(1) fib(1) fib(0) 9 calls 7 calls

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RUBYCONF 2020 • ARIEL CAPLAN • @AMCAPLAN • Fibonacci Performance hash[4] hash[0] hash[1] hash[3] hash[2] fib(4) fib(2) fib(1) fib(0) fib(3) fib(2) fib(1) fib(1) fib(0) fib(5) fib(1) fib(3) fib(2) fib(1) fib(0) hash[5] hash[1] hash[3] hash[2] 15 calls 9 calls

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RUBYCONF 2020 • ARIEL CAPLAN • @AMCAPLAN • Fibonacci Performance hash[4] hash[0] hash[1] hash[3] hash[2] fib(4) fib(2) fib(1) fib(0) fib(3) fib(2) fib(1) fib(1) fib(0) fib(5) fib(1) fib(3) fib(2) fib(1) fib(0) hash[5] hash[1] hash[3] hash[2] 25 calls 11 calls fib(6) fib(4) fib(2) fib(1) fib(0) fib(3) fib(2) fib(1) fib(1) fib(0) hash[6] hash[4]

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RUBYCONF 2020 • ARIEL CAPLAN • @AMCAPLAN • Fibonacci Performance 29,860,703 calls 69 calls fib(35) hash[35]

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RUBYCONF 2020 • ARIEL CAPLAN • @AMCAPLAN • Conway’s Game of Life def life_func(x, y, step) if step == 0 INITIAL_STATES[[x, y]] || 0 else neighbor_diffs = [[-1, -1], [-1, 0], [-1, 1], [ 0, -1], [ 0, 1], [ 1, -1], [ 1, 0], [ 1, 1]] live_neighbors = neighbor_diffs.sum { |x_diff, y_diff| life_func((x + x_diff) % WIDTH, (y + y_diff) % HEIGHT, step - 1) } if life_func(x, y, step - 1) == 1 [2, 3].include?(live_neighbors) ? 1 : 0 else live_neighbors == 3 ? 1 : 0 end end end

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RUBYCONF 2020 • ARIEL CAPLAN • @AMCAPLAN • Conway’s Game of Life life_hash = Hash.new do |h, (x, y, step)| h[[x, y, step]] = if step == 0 INITIAL_STATES[[x, y]] || 0 else neighbor_diffs = [[-1, -1], [-1, 0], [-1, 1], [ 0, -1], [ 0, 1], [ 1, -1], [ 1, 0], [ 1, 1]] live_neighbors = neighbor_diffs.sum { |x_diff, y_diff| h[[(x + x_diff) % WIDTH, (y + y_diff) % HEIGHT, step - 1]] } if h[[x, y, step - 1]] == 1 [2, 3].include?(live_neighbors) ? 1 : 0 else live_neighbors == 3 ? 1 : 0 end end end

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RUBYCONF 2020 • ARIEL CAPLAN • @AMCAPLAN • Conway’s Game of Life life_hash = Hash.new do |h, (x, y, step)| h[[x, y, step]] = if step == 0 INITIAL_STATES[[x, y]] || 0 else neighbor_diffs = [[-1, -1], [-1, 0], [-1, 1], [ 0, -1], [ 0, 1], [ 1, -1], [ 1, 0], [ 1, 1]] live_neighbors = neighbor_diffs.sum { |x_diff, y_diff| h[[(x + x_diff) % WIDTH, (y + y_diff) % HEIGHT, step - 1]] } if h[[x, y, step - 1]] == 1 [2, 3].include?(live_neighbors) ? 1 : 0 else live_neighbors == 3 ? 1 : 0 end end end def life_func(x, y, step) if step == 0 INITIAL_STATES[[x, y]] || 0 else neighbor_diffs = [[-1, -1], [-1, 0], [-1, 1], [ 0, -1], [ 0, 1], [ 1, -1], [ 1, 0], [ 1, 1]] live_neighbors = neighbor_diffs.sum { |x_diff, y_diff| life_func((x + x_diff) % WIDTH, (y + y_diff) % HEIGHT, step - 1) } if life_func(x, y, step - 1) == 1 [2, 3].include?(live_neighbors) ? 1 : 0 else live_neighbors == 3 ? 1 : 0 end end end

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RUBYCONF 2020 • ARIEL CAPLAN • @AMCAPLAN • Conway’s Game of Life

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RUBYCONF 2020 • ARIEL CAPLAN • @AMCAPLAN • talk[:defaults][:abbrev]

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RUBYCONF 2020 • ARIEL CAPLAN • @AMCAPLAN • Abbrev require 'abbrev' Abbrev.abbrev(["conf", "code"]) #=> {"conf"=>"conf", "con"=>"conf", "code"=>"code", "cod"=>"code"}

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RUBYCONF 2020 • ARIEL CAPLAN • @AMCAPLAN • Abbrev def abbrev(words, pattern = nil) table = {} seen = Hash.new(0) if pattern.is_a?(String) pattern = /\A#{Regexp.quote(pattern)}/ # regard as a prefix end words.each do |word| next if word.empty? word.size.downto(1) { |len| abbrev = word[0...len] next if pattern && pattern !~ abbrev case seen[abbrev] += 1 when 1 table[abbrev] = word when 2 table.delete(abbrev) else break end } end words.each do |word| next if pattern && pattern !~ word table[word] = word end table end

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RUBYCONF 2020 • ARIEL CAPLAN • @AMCAPLAN • Abbrev Seen Table conf => conf

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RUBYCONF 2020 • ARIEL CAPLAN • @AMCAPLAN • Abbrev Seen Table conf => conf conf 1 => conf

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RUBYCONF 2020 • ARIEL CAPLAN • @AMCAPLAN • Abbrev Seen Table conf => conf conf 1 con => conf

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RUBYCONF 2020 • ARIEL CAPLAN • @AMCAPLAN • Abbrev Seen Table conf => conf conf 1 con con 1 => conf => conf

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RUBYCONF 2020 • ARIEL CAPLAN • @AMCAPLAN • Abbrev Seen Table conf conf 1 con con 1 co co 1 c c 1 => conf => conf => conf => conf code => code

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RUBYCONF 2020 • ARIEL CAPLAN • @AMCAPLAN • Abbrev Seen Table conf conf 1 con con 1 co co 1 c c 1 => conf => conf => conf => conf code => code code 1 => code cod cod 1 => code co

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RUBYCONF 2020 • ARIEL CAPLAN • @AMCAPLAN • Abbrev Seen Table conf conf 1 con con 1 co co 1 c c 1 => conf => conf => conf => conf code => code code 1 => code cod cod 1 => code co 2

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RUBYCONF 2020 • ARIEL CAPLAN • @AMCAPLAN • Abbrev Seen Table conf conf 1 con con 1 co 1 c c 1 => conf => conf => conf code => code code 1 => code cod cod 1 => code 2

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RUBYCONF 2020 • ARIEL CAPLAN • @AMCAPLAN • Abbrev Seen Table conf conf 1 con con 1 co 1 c c 1 => conf => conf => conf code => code code 1 => code cod cod 1 => code 2 c

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RUBYCONF 2020 • ARIEL CAPLAN • @AMCAPLAN • Abbrev Seen Table conf conf 1 con con 1 co 1 c 1 => conf => conf code => code code 1 => code cod cod 1 => code 2 2

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RUBYCONF 2020 • ARIEL CAPLAN • @AMCAPLAN • Abbrev def abbrev(words) table = {} seen = Hash.new(0) words.each do |word| word.size.downto(1) { |len| abbrev = word[0...len] case seen[abbrev] += 1 when 1 table[abbrev] = word when 2 table.delete(abbrev) else break end } end table end Default Value Return Value Add Abbreviations Seen Once Remove Ambiguous Abbreviations Never set seen[abbrev] to 0! Iterate over each word portion

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RUBYCONF 2020 • ARIEL CAPLAN • @AMCAPLAN • talk[:defaults][:app_code]

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RUBYCONF 2020 • ARIEL CAPLAN • @AMCAPLAN • Abbrev-like Default Value totals = Hash.new(0) items = ["a", "a", "b", "c", "c", "c", "d", "b"] items.each { |item| totals[item] += 1 } totals #=> {"a"=>2, "b"=>2, "c"=>3, "d"=>1} totals["e"] #=> 0

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RUBYCONF 2020 • ARIEL CAPLAN • @AMCAPLAN • Real-Life Defaults! totals = Hash.new(0) # { "sum" => 1000 } by_company = Hash.new { |h,k| h[k] = Hash.new(0) } # { "a_company" => { "sum" => 100 }} totals["unset_key"] #=> 0 by_company["some_company"]["sum"] #=> 0

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RUBYCONF 2020 • ARIEL CAPLAN • @AMCAPLAN • Real-Life Defaults! def some_expensive_calculation @some_expensive_calculation ||= _do_the_expensive_calculation end

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RUBYCONF 2020 • ARIEL CAPLAN • @AMCAPLAN • Real-Life Defaults! def some_expensive_calculation_a @some_expensive_calculation_a ||= _do_the_expensive_calculation(:a) end def some_expensive_calculation_b @some_expensive_calculation_b ||= _do_the_expensive_calculation(:b) end def some_expensive_calculation_c @some_expensive_calculation_c ||= _do_the_expensive_calculation(:c) end

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RUBYCONF 2020 • ARIEL CAPLAN • @AMCAPLAN • Real-Life Defaults! def some_expensive_calculation(argument) @some_expensive_calculation ||= Hash.new do |h, k| h[k] = _do_the_expensive_calculation(k) end @some_expensive_calculation[argument] end

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RUBYCONF 2020 • ARIEL CAPLAN • @AMCAPLAN • •Flexibility: any object can be a key or value •Dynamicity and Resilience: default value/proc •Recursion-ish •Caching strategies What have we covered?

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RUBYCONF 2020 • ARIEL CAPLAN • @AMCAPLAN • Please say hi in the Slack chat!