Set is much faster than array for checking uniqueness

[jrafanie]

Specifically, when we call Array#include? to check if we've already
visited a node, Set is much faster especially as the number of nodes
visited increases.

It's probably neglible for most use cases but there is a difference.

Benchmark results: Array is between 1.42x and 3.57x slower than Set
in DeepDup with ruby 2.3.4.

$ ruby benchmark.rb
Warming up --------------------------------------
Small hash - Array way
                        33.169k i/100ms
Small hash - Set way    25.883k i/100ms
Calculating -------------------------------------
Small hash - Array way
                        379.253k (± 3.3%) i/s -      1.924M in   5.078544s
Small hash - Set way    266.919k (± 7.9%) i/s -      1.346M in   5.077567s

Comparison:
Small hash - Array way:   379253.4 i/s
Small hash - Set way:   266919.4 i/s - 1.42x  slower

Warming up --------------------------------------
Large hash - Array way
                        20.000  i/100ms
Large hash - Set way    67.000  i/100ms
Calculating -------------------------------------
Large hash - Array way
                        218.159  (± 4.6%) i/s -      1.100k in   5.052188s
Large hash - Set way    779.445  (± 8.0%) i/s -      3.886k in   5.019390s

Comparison:
Large hash - Set way:      779.4 i/s
Large hash - Array way:      218.2 i/s - 3.57x  slower

Benchmark script:

require 'yaml'
require "net/http"
require "uri"

uri = URI.parse("https://raw.githubusercontent.com/ManageIQ/manageiq/95130f3360a4abd82128ad2c23550d837799bb45/locale/en.yml")
response = Net::HTTP.get_response(uri)

large_hash = YAML.load(response.body)
small_hash = { :a => { :b => 'c' } }

require "benchmark/ips"
require 'set'

class DeepDupOriginal
  def initialize(opts={})
    @recurse_over_arrays = opts.fetch(:recurse_over_arrays, false)
    @preserve_original_keys = opts.fetch(:preserve_original_keys, false)
  end

  def call(obj)
    deep_dup(obj)
  end

  private

  def deep_dup(obj, visited=[])
    if obj.is_a?(Hash)
      obj.each_with_object({}) do |(key, value), h|
        h[@preserve_original_keys ? key : key.to_sym] = value_or_deep_dup(value, visited)
      end
    elsif obj.is_a?(Array) && @recurse_over_arrays
      obj.each_with_object([]) do |value, arr|
        value = value.is_a?(RecursiveOpenStruct) ? value.to_h : value
        arr << value_or_deep_dup(value, visited)
      end
    else
      obj
    end
  end

  def value_or_deep_dup(value, visited)
    obj_id = value.object_id
    visited.include?(obj_id) ? value : deep_dup(value, visited << obj_id)
  end
end

class DeepDupSet
  def initialize(opts={})
    @recurse_over_arrays = opts.fetch(:recurse_over_arrays, false)
    @preserve_original_keys = opts.fetch(:preserve_original_keys, false)
  end

  def call(obj)
    deep_dup(obj)
  end

  private

  def deep_dup(obj, visited=Set.new)
    if obj.is_a?(Hash)
      obj.each_with_object({}) do |(key, value), h|
        h[@preserve_original_keys ? key : key.to_sym] = value_or_deep_dup(value, visited)
      end
    elsif obj.is_a?(Array) && @recurse_over_arrays
      obj.each_with_object([]) do |value, arr|
        value = value.is_a?(RecursiveOpenStruct) ? value.to_h : value
        arr << value_or_deep_dup(value, visited)
      end
    else
      obj
    end
  end

  def value_or_deep_dup(value, visited)
    obj_id = value.object_id
    visited.include?(obj_id) ? value : deep_dup(value, visited << obj_id)
  end
end

Benchmark.ips do |x|
  x.report("Small hash - Array way") { DeepDupOriginal.new.call(small_hash)}
  x.report("Small hash - Set way")   { DeepDupSet.new.call(small_hash)}
  x.compare!
end

Benchmark.ips do |x|
  x.report("Large hash - Array way") { DeepDupOriginal.new.call(large_hash)}
  x.report("Large hash - Set way")   { DeepDupSet.new.call(large_hash)}
  x.compare!
end

[aetherknight]

Looks good. I'll get it merged in and cut a new release in a moment.