Regex Backslash D vs 0-9

require 'benchmark'

Benchmark.bm(7) do |x|
  STR = 'l2yanS'
  REGEX1 = /^(?=.*[a-z])(?=.*[A-Z])[a-zA-Z\d]{6}$/
  REGEX2 = /^(?=.*[a-z])(?=.*[A-Z])[0-9a-zA-Z]{6}$/
  x.report("Using backslash d:") { 1_000_000.times do
    STR =~ REGEX1
 end }
  x.report("Using 0-9:") { 1_000_000.times do
    STR =~ REGEX2
  end }
end

# RESULTS
                     user     system      total        real
Using backslash d:  0.450000   0.010000   0.460000 (  0.453032)
Using 0-9:           0.470000   0.000000   0.470000 (  0.475317)