01_clever_vs_unclever.rb

require "benchmark/ips"

NUMBERS = (0..100).to_a.shuffle
STRINGS = ("abcd".."efgh").to_a.shuffle

def val
  case rand(0..1)
  when 0 then NUMBERS.sample
  else STRINGS.sample
  end
end

def clever(arr)
  arr.reject &String.method(:===)
end

def unclever(arr)
  arr.reject {|s| String === s }
end

vals = Array.new(10000) { val }

Benchmark.ips do |x|
  x.report("clever") { clever(vals) }
  x.report("unclever") { unclever(vals) }
  x.compare!
end

02_result.txt

$ ruby -v
ruby 2.3.1p112 (2016-04-26 revision 54768) [x86_64-darwin15]

$ ruby 01_clever_vs_unclever.rb
Warming up --------------------------------------
              clever   109.000  i/100ms
            unclever   126.000  i/100ms
Calculating -------------------------------------
              clever      1.110k (± 2.4%) i/s -      5.559k in   5.012965s
            unclever      1.297k (± 3.6%) i/s -      6.552k in   5.058913s

Comparison:
            unclever:     1297.0 i/s
              clever:     1109.6 i/s - 1.17x  slower