string_alloc_test

string_alloc_test.rb

require "mkmf"

create_makefile("string_alloc_test")
raise "Unable to compile" unless system("make")

require_relative "string_alloc_test.so"
require "benchmark/ips"
include StringAllocTest

def r_alloc
  "abcdef"
end

@str = nil
def r_reuse
  @str ||= "abcdef"
end

def r_freeze
  -"abcdef"
end

Benchmark.ips do |x|
  x.time = 0.2
  x.warmup = 0.1

  puts "ruby #{RUBY_VERSION}"
  [:c_alloc, :c_reuse, :r_alloc, :r_reuse, :r_freeze].each do |m|
    p [send(m), send(m).object_id, send(m), send(m).object_id]
    x.report(m, m.to_s)
  end
  x.report("new string literal", '"abcdef"')
  x.report("reuse string literal", '-"abcdef"')
end

• How is calling :r_alloc different from '"abcdef"' ? (calling overhead?)

Exactly, it's with and without the method call.

• Is x.report(m, m.to_s) equivalent to x.report(m) { send(m) } ?

Similar it's with and without the block invocation, see here.

I think you should also compare with frozen_string_literal pragma and calling String.new("abcdef") and calling +"abcdef"

Feel free to fork and add more variations. For me the comparison between c_alloc and c_reuse was the most interesting part. I extended the C part a bit more to add somewhat more variation to the st_table. It slowed down r_reuse somewhat, but it was still faster than creation of new strings.

Thank you for the clarifications :)