Add frozen_string_literal comment

[elebow]

This change adds frozen_string_literal: true. Frozen strings are allocated once at parse-time and reused. This saves a substantial number of memory allocations and String instantiations. This magic comment is safe to use in all versions of Ruby.

Benchmarking using the same snippet as in #12 shows a 1.2% speedup in line generation. Note that these benchmarks were performed with #12 applied.

require "benchmark"

Benchmark.bmbm do |bm_out|
	bm_out.report { 5_000_000.times { CSVSafe.generate_line(["|yes", "no"]) } }
end

Legacy:

       user     system      total        real
  89.457235   0.255369  89.712604 ( 89.747471)

This branch:

       user     system      total        real
  88.287842   0.264821  88.552663 ( 88.604517)

The #starts_with_special_character? method itself is about 37% faster, using a similar benchmark.

[elebow]

Some smarter benchmarks, using the library more effectively:

csvsafe = CSVSafe.new($stderr, encoding: Encoding.find("utf-8"))

Benchmark.bmbm do |bm_out|
  bm_out.report { 5_000_000.times { csvsafe << ["|yes", "no"] } }
end

baseline:

       user     system      total        real
  22.137823   3.364592  25.502415 ( 25.550722)

start_with? (6.3% faster than baseline):

       user     system      total        real
  20.558799   3.466152  24.024951 ( 24.083241)

start_with? and frozen_string_literal (14.5% faster than baseline):

       user     system      total        real
  18.554075   3.299231  21.853306 ( 21.910121)

[zvory]

thank you

[zvory]

rolled out in #14 and released to rubygems.

[zvory]

@elebow just curious, where do you use csv-safe?

[elebow]

We use csv-safe in several products at Cofense to ensure generated CSVs behave predictably in Excel.