Conditional string building in Ruby

benchmark.rb

#!/usr/bin/env ruby

# gem install benchmark-ips benchmark-memory
# ruby benchmark.rb

require "benchmark/ips"
require "benchmark/memory"

Benchmark.ips do |x|
	x.report("join") do
		blah = []
		blah << "cancelled"
		blah << "(reason)" if 1.odd?
		blah.join(" ")
	end
	x.report("tap") do
		"cancelled".tap do |s|
			s << " (reason)" if 1.odd?
		end
	end

	x.compare!
end

Benchmark.memory do |x|
	x.report("join") do
		blah = []
		blah << "cancelled"
		blah << "(reason)" if 1.odd?
		blah.join(" ")
	end
	x.report("tap") do
		"cancelled".tap do |s|
			s << " (reason)" if 1.odd?
		end
	end

	x.compare!
end

# ruby 2.2.3p173
# Warming up --------------------------------------
#                 join    69.404k i/100ms
#                  tap   118.522k i/100ms
# Calculating -------------------------------------
#                 join    957.332k (± 3.4%) i/s -      4.789M in   5.008177s
#                  tap      2.105M (± 3.5%) i/s -     10.548M in   5.016827s
# 
# Comparison:
#                  tap:  2105236.9 i/s
#                 join:   957331.5 i/s - 2.20x  slower
# 
# Calculating -------------------------------------
#                 join   329.000  memsize (     0.000  retained)
#                          5.000  objects (     0.000  retained)
#                          4.000  strings (     0.000  retained)
#                  tap    80.000  memsize (     0.000  retained)
#                          2.000  objects (     0.000  retained)
#                          2.000  strings (     0.000  retained)
# 
# Comparison:
#                  tap:         80 allocated
#                 join:        329 allocated - 4.11x more

# ruby 2.4.0p0
# Warming up --------------------------------------
#                 join    83.091k i/100ms
#                  tap   153.893k i/100ms
# Calculating -------------------------------------
#                 join      1.127M (± 3.3%) i/s -      5.650M in   5.017113s
#                  tap      2.918M (± 4.1%) i/s -     14.620M in   5.019061s
# 
# Comparison:
#                  tap:  2917894.7 i/s
#                 join:  1127426.0 i/s - 2.59x  slower
# 
# Calculating -------------------------------------
#                 join   328.000  memsize (     0.000  retained)
#                          5.000  objects (     0.000  retained)
#                          4.000  strings (     0.000  retained)
#                  tap    80.000  memsize (     0.000  retained)
#                          2.000  objects (     0.000  retained)
#                          2.000  strings (     0.000  retained)
# 
# Comparison:
#                  tap:         80 allocated
#                 join:        328 allocated - 4.10x more