Ruby: Compare Hash direct assignment vs merge

hash_assign_vs_merge.rb

#!/usr/bin/env ruby
# frozen_string_literal: true

require "benchmark/ips"

hash1 = {}
hash2 = {}

Benchmark.ips do |x|
  x.report("assign") do
    hash1["X-Custom"] = "foo"
  end

  x.report("merge") do
    hash2.merge!("X-Custom" => "foo")
  end

  x.compare!
end

__END__
Results:

    Warming up --------------------------------------
                  assign     1.175M i/100ms
                   merge   471.783k i/100ms
    Calculating -------------------------------------
                  assign     11.856M (± 3.1%) i/s -     59.904M in   5.058411s
                   merge      4.719M (± 2.2%) i/s -     23.589M in   5.001957s

    Comparison:
                  assign: 11855616.8 i/s
                   merge:  4718589.0 i/s - 2.51x  (± 0.00) slower

Ruby:

    ruby 3.1.0p0 (2021-12-25 revision fb4df44d16) [x86_64-darwin21]

Hardware:

    Hardware Overview:

      Model Name: MacBook Pro
      Model Identifier: MacBookPro16,2
      Processor Name: Quad-Core Intel Core i7
      Processor Speed: 2,3 GHz
      Number of Processors: 1
      Total Number of Cores: 4
      L2 Cache (per Core): 512 KB
      L3 Cache: 8 MB
      Hyper-Threading Technology: Enabled
      Memory: 32 GB
      System Firmware Version: 1715.81.2.0.0 (iBridge: 19.16.10744.0.0,0)
      OS Loader Version: 540.80.2~11

Software:

    System Software Overview:

      System Version: macOS 12.2.1 (21D62)
      Kernel Version: Darwin 21.3.0
      Time since boot: 1 day 5:14