bench_ivar_warn.rb

require 'benchmark/ips'

$VERBOSE = true

# initialized
class A
  def initialize
    @c = @d = @e = @f = @g = @h = nil
  end
  def b
    @c || @d || @e || @f || @g || @h
  end
end

# not initialized
class B
  def initialize
    # nothing
  end
  def b
    @c || @d || @e || @f || @g || @h
  end
  def expected_uninitialized_instance_variable?(iv)
    true
  end
end

AI = A.new
BI = B.new

Benchmark.ips do |x|
  x.iterations = 2
  x.report('initialized') { AI.b }
  x.report('uninitialized') { BI.b }
  x.compare!
end

results.txt

$ ruby bench_ivar_warn.rb
Warming up --------------------------------------
         initialized     1.484M i/100ms
       uninitialized   223.758k i/100ms
         initialized     1.435M i/100ms
       uninitialized   224.504k i/100ms
Calculating -------------------------------------
         initialized     14.718M (± 1.6%) i/s -     74.597M in   5.069779s
       uninitialized      2.234M (± 0.6%) i/s -     11.225M in   5.023918s
         initialized     14.755M (± 1.5%) i/s -     74.597M in   5.057123s
       uninitialized      2.227M (± 1.8%) i/s -     11.225M in   5.041341s

Comparison:
         initialized: 14754531.3 i/s
       uninitialized:  2227414.1 i/s - 6.62x  (± 0.00) slower