do not compile regexp on every call

activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb

@@ -64,27 +64,25 @@ def cast_hstore(object)
         end
 
         private
+        HSTORE_ESCAPE = {
+            ' '  => '\\ ',
+            '\\' => '\\\\',
+            '"'  => '\\"',
+            '='  => '\\=',
+        }
+        HSTORE_ESCAPE_RE   = Regexp.union(HSTORE_ESCAPE.keys)
+        HSTORE_UNESCAPE    = HSTORE_ESCAPE.invert
+        HSTORE_UNESCAPE_RE = Regexp.union(HSTORE_UNESCAPE.keys)
+
         def unescape_hstore(value)
-          escape_values = {
-            '\\ '  => ' ',
-            '\\\\' => '\\',
-            '\\"'  => '"',
-            '\\='  => '=',
-          }
-          value.gsub(Regexp.union(escape_values.keys)) do |match|
-            escape_values[match]
+          value.gsub(HSTORE_UNESCAPE_RE) do |match|
+            HSTORE_UNESCAPE[match]
           end
         end
 
         def escape_hstore(value)
-          escape_values = {
-            ' '  => '\\ ',
-            '\\' => '\\\\',
-            '"'  => '\\"',
-            '='  => '\\=',
-          }
-          value.gsub(Regexp.union(escape_values.keys)) do |match|
-            escape_values[match]
+          value.gsub(HSTORE_ESCAPE_RE) do |match|
+            HSTORE_ESCAPE[match]
           end
         end
       end