Each, each_with_object, inject, merge Array to Hash transforming comparison

array2hash_each_inject_etc.rb

Warming up --------------------------------------
       assign&return    21.225k i/100ms
                each    23.473k i/100ms
               merge     3.283k i/100ms
              merge!     9.870k i/100ms
     map with tuples    19.764k i/100ms
    each_with_object    21.362k i/100ms
Calculating -------------------------------------
       assign&return    229.939k (± 5.2%) i/s -      2.314M in  10.087643s
                each    256.244k (± 7.3%) i/s -      2.559M in  10.028367s
               merge     33.238k (± 4.4%) i/s -    334.866k in  10.093927s
              merge!    101.249k (± 5.1%) i/s -      1.017M in  10.065749s
     map with tuples    211.932k (± 4.3%) i/s -      2.135M in  10.089963s
    each_with_object    231.771k (± 6.1%) i/s -      2.328M in  10.081857s

Comparison:
                each:   256244.3 i/s
    each_with_object:   231771.0 i/s - same-ish: difference falls within error
       assign&return:   229938.5 i/s - same-ish: difference falls within error
     map with tuples:   211932.0 i/s - 1.21x slower
              merge!:   101249.3 i/s - 2.53x slower
               merge:    33238.1 i/s - 7.71x slower


Code:
-----------------------------
# frozen_string_literal: true

# Install the necessary gems:
# gem install benchmark-ips
# gem install kalibera

require 'benchmark/ips'

# Enable and start GC before each job run. Disable GC afterwards.
#
# Inspired by https://www.omniref.com/ruby/2.2.1/symbols/Benchmark/bm?#annotation=4095926&line=182
class GCSuite
  def warming(*)
    run_gc
  end

  def running(*)
    run_gc
  end

  def warmup_stats(*)
  end

  def add_report(*)
  end

  private

  def run_gc
    GC.enable
    GC.start
    GC.disable
  end
end

suite = GCSuite.new

User = Struct.new(:id, :stuff)
a = Array.new(10) { |i| User.new(i, stuff: rand(1000)) }

Benchmark.ips do |x|
  x.config(:time => 10, :warmup => 5, :stats => :bootstrap, :confidence => 95)

  x.report('assign&return') do
    a.inject({}) { |memo, i| memo[i.id] = i.stuff; memo }
  end

  x.report('each') do
    memo = {}
    a.each { |i| memo[i.id] = i.stuff }
    memo
  end

  x.report('merge') do
    a.inject({}) { |memo, i| memo.merge(i.id => i.stuff) }
  end

  x.report('merge!') do
    a.inject({}) { |memo, i| memo.merge!(i.id => i.stuff) }
  end

  x.report('map with tuples') do
    a.map { |i| [i.id, i.stuff] }.to_h
  end

  x.report('each_with_object') do
    a.each_with_object({}) { |i, memo| memo[i.id] = i.stuff }
  end

  x.compare!
end