Array#to_proc, shorthand for creating a block that selects elements of an array/hash/collection.

array_to_proc.rb

class Array

  # Returns a proc which calls [] with the array's contents as arguments
  #
  # ====Usage
  #   [[1, 2], [3, 4], [5, 6]].map(&[0])
  #   # => [1, 3, 5]
  #
  #   [{ hello: 'world' }, { hello: 'sun', goodbye: 'moon' }].map(&[:hello])
  #   # => ['world', 'sun']
  #
  #   [[1, 2, 3, 4], [5, 6, 7]].map(&[1..-1])
  #   # => [[2, 3, 4], [6, 7]]
  def to_proc
    Proc.new { |obj| obj[*self] }
  end

end