.rb

require 'benchmark/ips'

LONG_STRING = "                           
                           
                           
                           
                                 "

NEW_REGEX = /[[:^space:]]/
OLD_REGEX = /\A[[:space:]]*\z/

def new_blank(str)
  str.empty? || !(NEW_REGEX === str)
end

def old_blank(str)
  str.empty? || OLD_REGEX === str
end

Benchmark.ips do |x|
  x.report('old') do |times| 
    i = 0
    while i < times
      old_blank(LONG_STRING)
      i += 1
    end
  end
  x.report('new') do |times| 
    i = 0
    while i < times
      new_blank(LONG_STRING)
      i += 1
    end
  end
  x.compare!
end

# Warming up --------------------------------------
#                  old    27.244k i/100ms
#                  new    19.854k i/100ms
# Calculating -------------------------------------
#                  old    317.945k (±11.0%) i/s -      1.580M in   5.032018s
#                  new    217.889k (±12.4%) i/s -      1.072M in   5.001483s

# Comparison:
#                  old:   317944.9 i/s
#                  new:   217889.3 i/s - 1.46x slower