bench.rb

# frozen_string_literal: true
require 'benchmark/ips'

Benchmark.ips do |x|
  x.report('+@') { +"" }
  x.report('new') { String.new }
  x.report('dup') { "".dup }
  x.compare!
end

result.txt

Warming up --------------------------------------
                  +@   439.631k i/100ms
                 new   387.940k i/100ms
                 dup   276.352k i/100ms
Calculating -------------------------------------
                  +@     11.340M (± 2.4%) i/s -     56.712M in   5.004134s
                 new      8.653M (± 1.7%) i/s -     43.449M in   5.022832s
                 dup      4.925M (± 4.6%) i/s -     24.595M in   5.007186s

Comparison:
                  +@: 11339997.4 i/s
                 new:  8652866.2 i/s - 1.31x  slower
                 dup:  4924670.0 i/s - 2.30x  slower