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)

6 files changed, 8 insertions, 8 deletions

diff --git a/activerecord/lib/active_record/attribute_methods.rb b/activerecord/lib/active_record/attribute_methods.rb
index 9d58a19304..abe1d465a5 100644
--- a/activerecord/lib/active_record/attribute_methods.rb
+++ b/activerecord/lib/active_record/attribute_methods.rb
@@ -42,7 +42,7 @@ module ActiveRecord
 
       def [](name)
         @method_cache.compute_if_absent(name) do
-          safe_name = name.unpack('h*').first
+          safe_name = name.unpack('h*'.freeze).first
           temp_method = "__temp__#{safe_name}"
           ActiveRecord::AttributeMethods::AttrNames.set_name_cache safe_name, name
           @module.module_eval method_body(temp_method, safe_name), __FILE__, __LINE__
diff --git a/activerecord/lib/active_record/attribute_methods/read.rb b/activerecord/lib/active_record/attribute_methods/read.rb
index 0d989c2eca..2363cf7608 100644
--- a/activerecord/lib/active_record/attribute_methods/read.rb
+++ b/activerecord/lib/active_record/attribute_methods/read.rb
@@ -37,7 +37,7 @@ module ActiveRecord
         protected
 
         def define_method_attribute(name)
-          safe_name = name.unpack('h*').first
+          safe_name = name.unpack('h*'.freeze).first
           temp_method = "__temp__#{safe_name}"
 
           ActiveRecord::AttributeMethods::AttrNames.set_name_cache safe_name, name
diff --git a/activerecord/lib/active_record/attribute_methods/write.rb b/activerecord/lib/active_record/attribute_methods/write.rb
index ab017c7b54..07d5e7d38e 100644
--- a/activerecord/lib/active_record/attribute_methods/write.rb
+++ b/activerecord/lib/active_record/attribute_methods/write.rb
@@ -24,7 +24,7 @@ module ActiveRecord
         protected
 
         def define_method_attribute=(name)
-          safe_name = name.unpack('h*').first
+          safe_name = name.unpack('h*'.freeze).first
           ActiveRecord::AttributeMethods::AttrNames.set_name_cache safe_name, name
 
           generated_attribute_methods.module_eval <<-STR, __FILE__, __LINE__ + 1
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/type_metadata.rb b/activerecord/lib/active_record/connection_adapters/postgresql/type_metadata.rb
index 58715978f7..b2c49989a4 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/type_metadata.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/type_metadata.rb
@@ -12,7 +12,7 @@ module ActiveRecord
       end
 
       def sql_type
-        super.gsub(/\[\]$/, "")
+        super.gsub(/\[\]$/, "".freeze)
       end
 
       def ==(other)
diff --git a/activerecord/lib/active_record/relation/delegation.rb b/activerecord/lib/active_record/relation/delegation.rb
index 86f2c30168..d75ec72b1a 100644
--- a/activerecord/lib/active_record/relation/delegation.rb
+++ b/activerecord/lib/active_record/relation/delegation.rb
@@ -18,7 +18,7 @@ module ActiveRecord
           delegate = Class.new(klass) {
             include ClassSpecificRelation
           }
-          const_set klass.name.gsub('::', '_'), delegate
+          const_set klass.name.gsub('::'.freeze, '_'.freeze), delegate
           cache[klass] = delegate
         end
       end
diff --git a/activerecord/lib/active_record/relation/predicate_builder.rb b/activerecord/lib/active_record/relation/predicate_builder.rb
index 43e9afe853..d26db7d4cf 100644
--- a/activerecord/lib/active_record/relation/predicate_builder.rb
+++ b/activerecord/lib/active_record/relation/predicate_builder.rb
@@ -52,7 +52,7 @@ module ActiveRecord
           key
         else
           key = key.to_s
-          key.split('.').first if key.include?('.')
+          key.split('.'.freeze).first if key.include?('.'.freeze)
         end
       end.compact
     end
@@ -123,10 +123,10 @@ module ActiveRecord
     end
 
     def convert_dot_notation_to_hash(attributes)
-      dot_notation = attributes.keys.select { |s| s.include?(".") }
+      dot_notation = attributes.keys.select { |s| s.include?(".".freeze) }
 
       dot_notation.each do |key|
-        table_name, column_name = key.split(".")
+        table_name, column_name = key.split(".".freeze)
         value = attributes.delete(key)
         attributes[table_name] ||= {}