BigDecimal to_s and yaml housekeeping

activesupport/lib/active_support/core_ext/bigdecimal/conversions.rb

@@ -4,35 +4,31 @@ module ActiveSupport #:nodoc:
   module CoreExtensions #:nodoc:
     module BigDecimal #:nodoc:
       module Conversions
+        DEFAULT_STRING_FORMAT = 'F'.freeze
+        YAML_TAG = 'tag:yaml.org,2002:float'.freeze
+        YAML_MAPPING = { 'Infinity' => '.Inf', '-Infinity' => '-.Inf', 'NaN' => '.NaN' }
+
         def self.included(base) #:nodoc:
-          base.instance_eval do
+          base.class_eval do
             alias_method :_original_to_s, :to_s
             alias_method :to_s, :to_formatted_s
+
+            yaml_as YAML_TAG
           end
         end
-        
-        def to_formatted_s(format="F")
+
+        def to_formatted_s(format = DEFAULT_STRING_FORMAT)
           _original_to_s(format)
         end
-        
-        yaml_as "tag:yaml.org,2002:float"
-        def to_yaml( opts = {} )
-          YAML::quick_emit( nil, opts ) do |out|
-            # This emits the number without any scientific notation.
-            # I prefer it to using self.to_f.to_s, which would lose precision.
-            #
-            # Note that YAML allows that when reconstituting floats
-            # to native types, some precision may get lost.
-            # There is no full precision real YAML tag that I am aware of.
-            str = self.to_s
-            if str == "Infinity"
-              str = ".Inf"
-            elsif str == "-Infinity"
-              str = "-.Inf"
-            elsif str == "NaN"
-              str = ".NaN"
-            end
-            out.scalar( "tag:yaml.org,2002:float", str, :plain )
+
+        # This emits the number without any scientific notation.
+        # This is better than self.to_f.to_s since it doesn't lose precision.
+        #
+        # Note that reconstituting YAML floats to native floats may lose precision.
+        def to_yaml(opts = {})
+          YAML.quick_emit(nil, opts) do |out|
+            string = to_s
+            out.scalar(YAML_TAG, YAML_MAPPING[string] || string, :plain)
           end
         end
       end