||= vs unless

bench.rb

require "benchmark/ips"

def fast
  test = nil

  test = 'test' unless test
  test = 'new test' unless test
end

def slow
  test = nil

  test ||= 'test'
  test ||= 'new test'
end

Benchmark.ips do |x|
  x.report("fast code description") { fast }
  x.report("slow code description") { slow }
  x.compare!
end


# Warming up --------------------------------------
# fast code description
#                        246.725k i/100ms
# slow code description
#                        237.570k i/100ms
# Calculating -------------------------------------
# fast code description
#                           6.824M (± 8.4%) i/s -     34.048M in   5.027930s
# slow code description
#                           6.475M (± 8.0%) i/s -     32.310M in   5.025982s
#
# Comparison:
# fast code description:  6824482.9 i/s
# slow code description:  6475027.7 i/s - same-ish: difference falls within error




# same but with class and instance variables
require "benchmark/ips"

class Fast
  def call
    @test = 'test' unless @test
    @test = 'new test' unless @test
  end
end

class Slow
  def call
    @test ||= 'test'
    @test ||= 'new test'
  end
end

Benchmark.ips do |x|
  x.report("fast code description") { Fast.new.call }
  x.report("slow code description") { Slow.new.call }
  x.compare!
end

# Warming up --------------------------------------
# fast code description
#                        187.973k i/100ms
# slow code description
#                        172.729k i/100ms
# Calculating -------------------------------------
# fast code description
#                           4.090M (± 7.3%) i/s -     20.489M in   5.038466s
# slow code description
#                           3.606M (± 7.6%) i/s -     17.964M in   5.014272s
#
# Comparison:
# fast code description:  4089680.8 i/s
# slow code description:  3606124.9 i/s - same-ish: difference falls within error