Ruby - Array.join versus String Concatenation (Efficiency)

Question

I recall getting a scolding for concatenating Strings in Python once upon a time. I was told that it is more efficient to create an List of Strings in Python and join them later

Answer 1

Try it yourself with the Benchmark class.

require "benchmark"

n = 1000000
Benchmark.bmbm do |x|
  x.report("concatenation") do
    foo = ""
    n.times do
      foo << "foobar"
    end
  end

  x.report("using lists") do
    foo = []
    n.times do
      foo << "foobar"
    end
    string = foo.join
  end
end

This produces the following output:

Rehearsal -------------------------------------------------
concatenation   0.300000   0.010000   0.310000 (  0.317457)
using lists     0.380000   0.050000   0.430000 (  0.442691)
---------------------------------------- total: 0.740000sec

                    user     system      total        real
concatenation   0.260000   0.010000   0.270000 (  0.309520)
using lists     0.310000   0.020000   0.330000 (  0.363102)

So it looks like concatenation is a little faster in this case. Benchmark on your system for your use-case.