Exploring #to_proc - Speaker Deck

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Exploring #to_proc

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Paul Mucur @mudge

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[:foo, :bar].map(&:to_s)

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[:foo, :bar].map(&:to_s)

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[1, 2, 3] #=> ["1", "2", "3"]

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result = [] [1, 2, 3].each do |number| result << number.to_s end

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[1, 2, 3].map do |number| number.to_s end

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[1, 2, 3].map { |number| number.to_s }

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[1, 2, 3].map(&:to_s)

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[1, 2, 3].map(&:to_s)

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[1, 2, 3].map(:to_s)

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“When you say names.map(&xxx), you’re telling Ruby to pass the Proc object in xxx to the map method as a block. If xxx isn’t already a Proc object, Ruby tries to coerce it into one by sending it a to_proc message.” — Dave Thomas, “Programming Ruby”

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[1, 2, 3].map(&:to_s.to_proc)

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:to_s.to_proc

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class Symbol def to_proc Proc.new { |obj| obj.send(self) } end end

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Proc.new { |obj| obj.send(:to_s) }

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Proc.new { |obj| obj.to_s }

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[1, 2, 3].map(&Proc.new { |obj| obj.to_s })

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[1, 2, 3].map { |obj| obj.to_s }

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[1, 2, 3].map { |number| number.to_s }

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http://railscasts.com/episodes/6-shortcut-blocks-with-symbol-to-proc

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http://railscasts.com/episodes/6-shortcut-blocks-with-symbol-to-proc

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“Elegance & familiarity are orthogonal.” — Rich Hickey

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http://thepugautomatic.com/2014/11/array-to-proc-for-hash-access/

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http://thepugautomatic.com/2014/11/array-to-proc-for-hash-access/

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“Maps are functions of their keys.” ! http://clojure.org/data_structures#Data Structures-Keywords

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“[Hashes] are functions of their keys.” ! http://clojure.org/data_structures#Data Structures-Keywords

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Input Output Function

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Domain Co-domain 1 2 3 A B C

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Hashes ! {:name "Bob", :age 42} {name: "Bob", age: 42}

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Key Value Function

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:name "Bob" Function

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Domain Co-domain :name :age "Bob" 42

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(def person {:name "Bob", :age 42}) ! ! ! ! !

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(def person {:name "Bob", :age 42}) ! (person :name) ! ! !

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(def person {:name "Bob", :age 42}) ! (person :name) ;;=> "Bob" ! !

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(def person {:name "Bob", :age 42}) ! (person :name) ;;=> "Bob" ! (person :height)

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(def person {:name "Bob", :age 42}) ! (person :name) ;;=> "Bob" ! (person :height) ;;=> nil

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(map even? [1 2 3 4])

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(map even? [1 2 3 4]) ;;=> (false true false true)

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(map person [:name :age])

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(map person [:name :age]) ;;=> ("Bob" 42)

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person = { name: "Bob", age: 42 } ! !

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person = { name: "Bob", age: 42 } ! name, age = [:name, :age].map(&person)

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person = { name: "Bob", age: 42 } ! name, age = [:name, :age].map(&person) #=> ["Bob", 42]

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[:yes, :yes, :no, :yes].map(&{yes: 1, no: 0}) http://blog.japila.pl/2011/01/maps-as-data-structures-in-clojure-are-functions-of-their-keys-a-nifty-use-case/

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[:yes, :yes, :no, :yes].map(&{yes: 1, no: 0}) #=> [1, 1, 0, 1] http://blog.japila.pl/2011/01/maps-as-data-structures-in-clojure-are-functions-of-their-keys-a-nifty-use-case/

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class Hash def to_proc Proc.new { |key| self[key] } end end

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class Hash def to_proc proc { |key| self[key] }! end end

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class Hash def to_proc method(:[]).to_proc end end

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Arrays ! ["A" "B" "C"] ["A", "B", "C"]

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Index Value Function

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0 "A" Function

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Domain Co-domain 0 1 2 "A" "B" "C"

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(def letters ["A" "B" "C"]) ! (letters 1)

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(def letters ["A" "B" "C"]) ! (letters 1) ;;=> "B"

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(map letters (range 1 3))

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(map letters (range 1 3)) ;;=> ("B" "C")

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letters = ["A", "B", "C"] ! (1...3).map(&letters)

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letters = ["A", "B", "C"] ! (1...3).map(&letters) #=> ["B", "C"]

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class Array def to_proc method(:[]).to_proc end end

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“Sets are functions of their members.” ! http://clojure.org/data_structures#Data Structures-Keywords

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Sets ! #{"Steve" "Michael"} Set["Steve", "Michael"]

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Member Member Function

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"Steve" "Steve" Function

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"Arnold" nil Function

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Domain Co-domain "Steve" "Michael" "Steve" "Michael"

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(def banned #{"Steve" "Michael"}) (def guest-‐list ["Brian" "Josh" "Steve"]) ! ! http://blog.jayﬁelds.com/2010/08/clojure-using-sets-and-maps-as.html

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(def banned #{"Steve" "Michael"}) (def guest-‐list ["Brian" "Josh" "Steve"]) ! (remove banned guest-‐list) http://blog.jayﬁelds.com/2010/08/clojure-using-sets-and-maps-as.html

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(def banned #{"Steve" "Michael"}) (def guest-‐list ["Brian" "Josh" "Steve"]) ! (remove banned guest-‐list) ;;=> ("Brian" "Josh") http://blog.jayﬁelds.com/2010/08/clojure-using-sets-and-maps-as.html

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banned = Set["Steve", "Michael"] guest_list = ["Brian", "Josh", "Steve"] ! !

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banned = Set["Steve", "Michael"] guest_list = ["Brian", "Josh", "Steve"] ! guest_list.reject(&banned)

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banned = Set["Steve", "Michael"] guest_list = ["Brian", "Josh", "Steve"] ! guest_list.reject(&banned) #=> ["Brian", "Josh"]

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class Set def to_proc proc { |element| element if member?(element) } end end

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Why?

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http://codon.com/a-lever-for-the-mind

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(g  ∘  f  )(x) = g(f(x))

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http://blog.jayﬁelds.com/2010/08/clojure-using-sets-and-maps-as.html old_orders = { 1 => 44, 2 => 33 } new_orders = { 1 => 55, 2 => 33 } ! ! ! ! ! ! ! ! ! !

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http://blog.jayﬁelds.com/2010/08/clojure-using-sets-and-maps-as.html old_orders = { 1 => 44, 2 => 33 } new_orders = { 1 => 55, 2 => 33 } ! require 'active_support/core_ext/hash/diff' old_orders.diff(new_orders).keys #=> [1] ! ! ! ! ! !

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http://blog.jayﬁelds.com/2010/08/clojure-using-sets-and-maps-as.html old_orders = { 1 => 44, 2 => 33 } new_orders = { 1 => 55, 2 => 33 } ! old_orders.dup. delete_if { |k, v| new_orders[k] == v }. merge!(new_orders.dup.delete_if { |k, v| old_orders.has_key?(k) }).keys #=> [1] ! ! ! ! !

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http://blog.jayﬁelds.com/2010/08/clojure-using-sets-and-maps-as.html old_orders = { 1 => 44, 2 => 33 } new_orders = { 1 => 55, 2 => 33 } ! order_differences = old_orders.merge(new_orders) { |_key, oldval, newval| oldval != newval } #=> {1=>true, 2=>false} ! ! ! ! !

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http://blog.jayﬁelds.com/2010/08/clojure-using-sets-and-maps-as.html old_orders = { 1 => 44, 2 => 33 } new_orders = { 1 => 55, 2 => 33 } ! Hash[new_orders.to_a -‐ old_orders.to_a].keys #=> [1] ! ! ! ! ! ! !

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One more thing…

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[1, 3, 4, 2].sort_by(&:-‐@) https://twitter.com/threedaymonk

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[1, 3, 4, 2].sort_by(&:-‐@) #=> [4, 3, 2, 1] https://twitter.com/threedaymonk

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http://raganwald.com/2007/11/fun-with-symboltoproc.html

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http://mudge.name/2014/11/26/data-structures-as-functions.html

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Thank you https://speakerdeck.com/mudge/exploring-number-to-proc