Freeze string literals when not mutated.

I wrote a utility that helps find areas where you could optimize your program using a frozen string instead of a string literal, it's called [let_it_go](https://github.com/schneems/let_it_go). After going through the output and adding `.freeze` I was able to eliminate the creation of 1,114 string objects on EVERY request to [codetriage](codetriage.com). How does this impact execution?

To look at memory:

```ruby
require 'get_process_mem'

mem = GetProcessMem.new
GC.start
GC.disable
1_114.times { " " }
before = mem.mb

after = mem.mb
GC.enable
puts "Diff: #{after - before} mb"

```

Creating 1,114 string objects results in `Diff: 0.03125 mb` of RAM allocated on every request. Or 1mb every 32 requests.

To look at raw speed:

```ruby
require 'benchmark/ips'

number_of_objects_reduced = 1_114

Benchmark.ips do |x|
  x.report("freeze")    { number_of_objects_reduced.times { " ".freeze } }
  x.report("no-freeze") { number_of_objects_reduced.times { " " } }
end
```

We get the results

```
Calculating -------------------------------------
              freeze     1.428k i/100ms
           no-freeze   609.000  i/100ms
-------------------------------------------------
              freeze     14.363k (± 8.5%) i/s -     71.400k
           no-freeze      6.084k (± 8.1%) i/s -     30.450k
```

Now we can do some maths:

```ruby
ips = 6_226k # iterations / 1 second
call_time_before = 1.0 / ips # seconds per iteration 

ips = 15_254 # iterations / 1 second
call_time_after = 1.0 / ips # seconds per iteration 

diff = call_time_before - call_time_after

number_of_objects_reduced * diff * 100

# => 0.4530373333993266 miliseconds saved per request
```

So we're shaving off 1 second of execution time for every 220 requests. 

Is this going to be an insane speed boost to any Rails app: nope. Should we merge it: yep. 

p.s. If you know of a method call that doesn't modify a string input such as [String#gsub](https://github.com/schneems/let_it_go/blob/b0e2da69f0cca87ab581022baa43291cdf48638c/lib/let_it_go/core_ext/string.rb#L37) please [give me a pull request to the appropriate file](https://github.com/schneems/let_it_go/blob/b0e2da69f0cca87ab581022baa43291cdf48638c/lib/let_it_go/core_ext/string.rb#L37), or open an issue in LetItGo so we can track and freeze more strings. 

Keep those strings Frozen

![](https://www.dropbox.com/s/z4dj9fdsv213r4v/let-it-go.gif?dl=1)

2 files changed, 11 insertions, 11 deletions

diff --git a/activesupport/lib/active_support/inflector/methods.rb b/activesupport/lib/active_support/inflector/methods.rb
index be369d21c6..5e95d2e5a5 100644
--- a/activesupport/lib/active_support/inflector/methods.rb
+++ b/activesupport/lib/active_support/inflector/methods.rb
@@ -91,10 +91,10 @@ module ActiveSupport
     def underscore(camel_cased_word)
       return camel_cased_word unless camel_cased_word =~ /[A-Z-]|::/
       word = camel_cased_word.to_s.gsub('::'.freeze, '/'.freeze)
-      word.gsub!(/(?:(?<=([A-Za-z\d]))|\b)(#{inflections.acronym_regex})(?=\b|[^a-z])/) { "#{$1 && '_'}#{$2.downcase}" }
-      word.gsub!(/([A-Z\d]+)([A-Z][a-z])/,'\1_\2')
-      word.gsub!(/([a-z\d])([A-Z])/,'\1_\2')
-      word.tr!("-", "_")
+      word.gsub!(/(?:(?<=([A-Za-z\d]))|\b)(#{inflections.acronym_regex})(?=\b|[^a-z])/) { "#{$1 && '_'.freeze }#{$2.downcase}" }
+      word.gsub!(/([A-Z\d]+)([A-Z][a-z])/, ' \1_\2'.freeze)
+      word.gsub!(/([a-z\d])([A-Z])/, '\1_\2'.freeze)
+      word.tr!("-".freeze, "_".freeze)
       word.downcase!
       word
     end
@@ -127,9 +127,9 @@ module ActiveSupport
 
       inflections.humans.each { |(rule, replacement)| break if result.sub!(rule, replacement) }
 
-      result.sub!(/\A_+/, '')
-      result.sub!(/_id\z/, '')
-      result.tr!('_', ' ')
+      result.sub!(/\A_+/, ''.freeze)
+      result.sub!(/_id\z/, ''.freeze)
+      result.tr!('_'.freeze, ' '.freeze)
 
       result.gsub!(/([a-z\d]*)/i) do |match|
         "#{inflections.acronyms[match] || match.downcase}"
@@ -178,14 +178,14 @@ module ActiveSupport
     #   classify('calculus')     # => "Calculu"
     def classify(table_name)
       # strip out any leading schema name
-      camelize(singularize(table_name.to_s.sub(/.*\./, '')))
+      camelize(singularize(table_name.to_s.sub(/.*\./, ''.freeze)))
     end
 
     # Replaces underscores with dashes in the string.
     #
     #   dasherize('puni_puni') # => "puni-puni"
     def dasherize(underscored_word)
-      underscored_word.tr('_', '-')
+      underscored_word.tr('_'.freeze, '-'.freeze)
     end
 
     # Removes the module part from the expression in the string.
@@ -248,7 +248,7 @@ module ActiveSupport
     # NameError is raised when the name is not in CamelCase or the constant is
     # unknown.
     def constantize(camel_cased_word)
-      names = camel_cased_word.split('::')
+      names = camel_cased_word.split('::'.freeze)
 
       # Trigger a built-in NameError exception including the ill-formed constant in the message.
       Object.const_get(camel_cased_word) if names.empty?
diff --git a/activesupport/lib/active_support/inflector/transliterate.rb b/activesupport/lib/active_support/inflector/transliterate.rb
index edea142e82..2c03956672 100644
--- a/activesupport/lib/active_support/inflector/transliterate.rb
+++ b/activesupport/lib/active_support/inflector/transliterate.rb
@@ -79,7 +79,7 @@ module ActiveSupport
         # No more than one of the separator in a row.
         parameterized_string.gsub!(/#{re_sep}{2,}/, sep)
         # Remove leading/trailing separator.
-        parameterized_string.gsub!(/^#{re_sep}|#{re_sep}$/i, '')
+        parameterized_string.gsub!(/^#{re_sep}|#{re_sep}$/i, ''.freeze)
       end
       parameterized_string.downcase
     end