Benchmark concatenating strings with reduce(:+) vs. with join('').

gistfile1.rb

require 'benchmark'

STRING = 'abc'
ITERATIONS = 500000

Benchmark.bm(10) do |bench|
  for n in [2,3,4, 5]
    n_strings = Array.new(n, STRING)

    bench.report("add  #{n}") do
      ITERATIONS.times do
        n_strings.reduce(:+)
      end
    end

    bench.report("join #{n}") do
      ITERATIONS.times do
        tmp = n_strings.join('')
      end
    end

    iteratable_dups = (0...ITERATIONS).map { n_strings.map(&:dup) }
    bench.report("append #{n}") do
      iteratable_dups.each do |dups|
        dups.reduce(:<<)
      end
    end

    puts "\n"
  end
end

ruby 1.9.2p290 (2011-07-09 revision 32553) [x86_64-darwin10.8.0]
ruby bench.rb

                user     system      total        real
add 2       0.270000   0.000000   0.270000 (  0.288561)
join 2      0.410000   0.000000   0.410000 (  0.408976)
append 2    0.340000   0.010000   0.350000 (  0.349376)

add 3       0.560000   0.000000   0.560000 (  0.573447)
join 3      1.120000   0.060000   1.180000 (  1.175387)
append 3    0.340000   0.010000   0.350000 (  0.361038)

add 4       0.430000   0.070000   0.500000 (  0.490610)
join 4      1.410000   0.060000   1.470000 (  1.513611)
append 4    0.400000   0.000000   0.400000 (  0.400209)

add 5       0.680000   0.010000   0.690000 (  0.683201)
join 5      1.500000   0.060000   1.560000 (  1.567156)
append 5    0.480000   0.000000   0.480000 (  0.477501)

ruby 1.9.3p0 (2011-10-30 revision 33570) [x86_64-darwin10.8.0]

ruby bench.rb 
                 user     system      total        real
add 2        0.280000   0.000000   0.280000 (  0.276870)
join 2       0.420000   0.000000   0.420000 (  0.426210)
append 2     0.310000   0.020000   0.330000 (  0.323369)

add 3        0.570000   0.000000   0.570000 (  0.587757)
join 3       1.150000   0.050000   1.200000 (  1.205024)
append 3     0.350000   0.020000   0.370000 (  0.365258)

add 4        0.470000   0.070000   0.540000 (  0.541062)
join 4       1.200000   0.030000   1.230000 (  1.249001)
append 4     0.410000   0.000000   0.410000 (  0.401136)

add 5        0.610000   0.000000   0.610000 (  0.620455)
join 5       1.550000   0.070000   1.620000 (  1.621642)
append 5     0.500000   0.010000   0.510000 (  0.491617)

ruby 1.9.3p125 (2012-02-16 revision 34643) [x86_64-darwin10.8.0]

add  2       0.280000   0.000000   0.280000 (  0.280966)
join 2       0.390000   0.000000   0.390000 (  0.390578)
append 2     0.340000   0.010000   0.350000 (  0.379686)

add  3       0.590000   0.010000   0.600000 (  0.637222)
join 3       1.130000   0.050000   1.180000 (  1.201451)
append 3     0.350000   0.020000   0.370000 (  0.376768)

add  4       0.480000   0.070000   0.550000 (  0.571988)
join 4       1.190000   0.030000   1.220000 (  1.265706)
append 4     0.420000   0.000000   0.420000 (  0.422308)

add  5       0.630000   0.000000   0.630000 (  0.638082)
join 5       1.520000   0.060000   1.580000 (  1.597781)
append 5     0.530000   0.010000   0.540000 (  0.546513)