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)

8 files changed, 20 insertions, 20 deletions

diff --git a/activesupport/lib/active_support/core_ext/load_error.rb b/activesupport/lib/active_support/core_ext/load_error.rb
index d9fb392752..60732eb41a 100644
--- a/activesupport/lib/active_support/core_ext/load_error.rb
+++ b/activesupport/lib/active_support/core_ext/load_error.rb
@@ -23,7 +23,7 @@ class LoadError
   # Returns true if the given path name (except perhaps for the ".rb"
   # extension) is the missing file which caused the exception to be raised.
   def is_missing?(location)
-    location.sub(/\.rb$/, '') == path.sub(/\.rb$/, '')
+    location.sub(/\.rb$/, ''.freeze) == path.sub(/\.rb$/, ''.freeze)
   end
 end
 
diff --git a/activesupport/lib/active_support/core_ext/module/delegation.rb b/activesupport/lib/active_support/core_ext/module/delegation.rb
index 9b7a429db9..9dc0dee1bd 100644
--- a/activesupport/lib/active_support/core_ext/module/delegation.rb
+++ b/activesupport/lib/active_support/core_ext/module/delegation.rb
@@ -167,7 +167,7 @@ class Module
         ''
       end
 
-    file, line = caller(1, 1).first.split(':', 2)
+    file, line = caller(1, 1).first.split(':'.freeze, 2)
     line = line.to_i
 
     to = to.to_s
diff --git a/activesupport/lib/active_support/dependencies.rb b/activesupport/lib/active_support/dependencies.rb
index 770c845435..fc6f822969 100644
--- a/activesupport/lib/active_support/dependencies.rb
+++ b/activesupport/lib/active_support/dependencies.rb
@@ -149,7 +149,7 @@ module ActiveSupport #:nodoc:
 
           # Normalize the list of new constants, and add them to the list we will return
           new_constants.each do |suffix|
-            constants << ([namespace, suffix] - ["Object"]).join("::")
+            constants << ([namespace, suffix] - ["Object"]).join("::".freeze)
           end
         end
         constants
@@ -431,7 +431,7 @@ module ActiveSupport #:nodoc:
 
     # Search for a file in autoload_paths matching the provided suffix.
     def search_for_file(path_suffix)
-      path_suffix = path_suffix.sub(/(\.rb)?$/, ".rb")
+      path_suffix = path_suffix.sub(/(\.rb)?$/, ".rb".freeze)
 
       autoload_paths.each do |root|
         path = File.join(root, path_suffix)
@@ -516,7 +516,7 @@ module ActiveSupport #:nodoc:
 
       if file_path
         expanded = File.expand_path(file_path)
-        expanded.sub!(/\.rb\z/, '')
+        expanded.sub!(/\.rb\z/, ''.freeze)
 
         if loading.include?(expanded)
           raise "Circular dependency detected while autoloading constant #{qualified_name}"
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
diff --git a/activesupport/lib/active_support/message_encryptor.rb b/activesupport/lib/active_support/message_encryptor.rb
index 92ab6fe648..c82a13511e 100644
--- a/activesupport/lib/active_support/message_encryptor.rb
+++ b/activesupport/lib/active_support/message_encryptor.rb
@@ -82,7 +82,7 @@ module ActiveSupport
 
     def _decrypt(encrypted_message)
       cipher = new_cipher
-      encrypted_data, iv = encrypted_message.split("--").map {|v| ::Base64.strict_decode64(v)}
+      encrypted_data, iv = encrypted_message.split("--".freeze).map {|v| ::Base64.strict_decode64(v)}
 
       cipher.decrypt
       cipher.key = @secret
diff --git a/activesupport/lib/active_support/message_verifier.rb b/activesupport/lib/active_support/message_verifier.rb
index b2a4404968..64c5232cf4 100644
--- a/activesupport/lib/active_support/message_verifier.rb
+++ b/activesupport/lib/active_support/message_verifier.rb
@@ -46,7 +46,7 @@ module ActiveSupport
     def valid_message?(signed_message)
       return if signed_message.nil? || !signed_message.valid_encoding? || signed_message.blank?
 
-      data, digest = signed_message.split("--")
+      data, digest = signed_message.split("--".freeze)
       data.present? && digest.present? && ActiveSupport::SecurityUtils.secure_compare(digest, generate_digest(data))
     end
 
@@ -74,7 +74,7 @@ module ActiveSupport
     def verified(signed_message)
       if valid_message?(signed_message)
         begin
-          data = signed_message.split("--")[0]
+          data = signed_message.split("--".freeze)[0]
           @serializer.load(decode(data))
         rescue ArgumentError => argument_error
           return if argument_error.message =~ %r{invalid base64}
diff --git a/activesupport/lib/active_support/multibyte/unicode.rb b/activesupport/lib/active_support/multibyte/unicode.rb
index 35efebc65f..f4de4a80d9 100644
--- a/activesupport/lib/active_support/multibyte/unicode.rb
+++ b/activesupport/lib/active_support/multibyte/unicode.rb
@@ -58,7 +58,7 @@ module ActiveSupport
       # Returns a regular expression pattern that matches the passed Unicode
       # codepoints.
       def self.codepoints_to_pattern(array_of_codepoints) #:nodoc:
-        array_of_codepoints.collect{ |e| [e].pack 'U*' }.join('|')
+        array_of_codepoints.collect{ |e| [e].pack 'U*'.freeze }.join('|'.freeze)
       end
       TRAILERS_PAT = /(#{codepoints_to_pattern(LEADERS_AND_TRAILERS)})+\Z/u
       LEADERS_PAT = /\A(#{codepoints_to_pattern(LEADERS_AND_TRAILERS)})+/u