Benchmark questionable code!

bench.rb

require 'benchmark/ips'
require 'benchmark/memory'

# IPS = iterations per second
# https://github.com/evanphx/benchmark-ips

string = "123"

%i[ips memory].each do |bench|
  puts bench.upcase
  Benchmark.send(bench) do |x|
    x.report("string match")    { string == "123" }
    x.report("classname match") { string.class.name == "String" }
    x.report("kind_of?")        { string.kind_of?(String) }
    x.report("is_a?")           { string.is_a?(String) }
    x.report("instance_of?")    { string.instance_of?(String) }
    x.compare!
  end
end

results.txt

IPS
Warming up --------------------------------------
        string match     1.273M i/100ms
     classname match   843.890k i/100ms
            kind_of?     1.722M i/100ms
               is_a?     1.726M i/100ms
        instance_of?     1.716M i/100ms
Calculating -------------------------------------
        string match     13.426M (± 2.3%) i/s -     67.481M in   5.028951s
     classname match      8.578M (± 1.7%) i/s -     43.038M in   5.019080s
            kind_of?     17.539M (± 2.7%) i/s -     87.847M in   5.012759s
               is_a?     17.578M (± 1.8%) i/s -     88.048M in   5.010710s
        instance_of?     17.442M (± 1.7%) i/s -     87.517M in   5.019161s

Comparison:
               is_a?: 17577715.9 i/s
            kind_of?: 17538697.9 i/s - same-ish: difference falls within error
        instance_of?: 17441575.0 i/s - same-ish: difference falls within error
        string match: 13425571.1 i/s - 1.31x  (± 0.00) slower
     classname match:  8577522.9 i/s - 2.05x  (± 0.00) slower

MEMORY
Calculating -------------------------------------
        string match    40.000  memsize (     0.000  retained)
                         1.000  objects (     0.000  retained)
                         1.000  strings (     0.000  retained)
     classname match    40.000  memsize (    40.000  retained)
                         1.000  objects (     1.000  retained)
                         1.000  strings (     1.000  retained)
            kind_of?     0.000  memsize (     0.000  retained)
                         0.000  objects (     0.000  retained)
                         0.000  strings (     0.000  retained)
               is_a?     0.000  memsize (     0.000  retained)
                         0.000  objects (     0.000  retained)
                         0.000  strings (     0.000  retained)
        instance_of?     0.000  memsize (     0.000  retained)
                         0.000  objects (     0.000  retained)
                         0.000  strings (     0.000  retained)

Comparison:
            kind_of?:          0 allocated
               is_a?:          0 allocated - same
        instance_of?:          0 allocated - same
        string match:         40 allocated - Infx more
     classname match:         40 allocated - Infx more