README.md

ruby 3.1.4p223 (2023-03-30 revision 957bb7cb81) [x86_64-darwin21]
Warming up --------------------------------------
       concatenation   449.658k i/100ms
          array join   249.847k i/100ms
Calculating -------------------------------------
       concatenation      4.375M (± 2.5%) i/s -     22.033M in   5.039031s
          array join      2.508M (± 4.3%) i/s -     12.742M in   5.090572s

Comparison:
       concatenation:  4375307.9 i/s
          array join:  2508357.4 i/s - 1.74x  slower

benchmark.rb

# frozen_string_literal: true

require "bundler/inline"

gemfile(true) do
  source "https://rubygems.org"

  gem "benchmark-ips"
end

first_name = "John"
last_name  = "Doe"

Benchmark.ips do |x|
  x.report("concatenation")  { "#{first_name} #{last_name}" }
  x.report("array join")     { [first_name, last_name].join(" ") }
  x.compare!
end