deserialize to RegexpOfHolding only when necessary

ext/cbson/cbson.c

@@ -62,6 +62,7 @@ static VALUE DBRef;
 static VALUE Code;
 static VALUE MinKey;
 static VALUE MaxKey;
+static VALUE Regexp;
 static VALUE RegexpOfHolding;
 static VALUE OrderedHash;
 static VALUE InvalidName;
@@ -693,8 +694,13 @@ static VALUE get_value(const char* buffer, int* position, int type) {
             }
             argv[0] = pattern;
             argv[1] = INT2FIX(flags);
-            argv[2] = rb_str_new2(extra);
-            value = rb_class_new_instance(3, argv, RegexpOfHolding);
+            if(extra[0] == 0) {
+                value = rb_class_new_instance(2, argv, Regexp);
+            }
+            else { // Deserializing a RegexpOfHolding
+                argv[2] = rb_str_new2(extra);
+                value = rb_class_new_instance(3, argv, RegexpOfHolding);
+            }
             *position += flags_length + 1;
             break;
         }
@@ -877,6 +883,7 @@ void Init_cbson() {
     MinKey = rb_const_get(mongo, rb_intern("MinKey"));
     MaxKey = rb_const_get(mongo, rb_intern("MaxKey"));
     rb_require("mongo/types/regexp_of_holding");
+    Regexp = rb_const_get(rb_cObject, rb_intern("Regexp"));
     RegexpOfHolding = rb_const_get(mongo, rb_intern("RegexpOfHolding"));
     rb_require("mongo/exceptions");
     InvalidName = rb_const_get(mongo, rb_intern("InvalidName"));

lib/mongo/util/bson_ruby.rb

@@ -329,7 +329,12 @@ class BSON_RUBY
     options |= Regexp::MULTILINE if options_str.include?('m')
     options |= Regexp::EXTENDED if options_str.include?('x')
     options_str.gsub!(/[imx]/, '') # Now remove the three we understand
-    RegexpOfHolding.new(str, options, options_str)
+    if options_str == ''
+      Regexp.new(str, options)
+    else
+      warn("Use deprecated Regexp options #{options_str}; future versions of this MongoDB driver will support only i, m, and x. See deprecated class RegexpOfHolding for more info.")
+      RegexpOfHolding.new(str, options, options_str)
+    end
   end
 
   def deserialize_string_data(buf)

test/test_bson.rb

@@ -138,10 +138,9 @@ class BSONTest < Test::Unit::TestCase
     assert_equal doc, doc2
 
     r = doc2['doc']
-    assert_kind_of RegexpOfHolding, r
-    assert_equal '', r.extra_options_str
+    assert_kind_of Regexp, r
 
-    r.extra_options_str << 'zywcab'
+    r = RegexpOfHolding.new('st', 0, 'zywcab')
     assert_equal 'zywcab', r.extra_options_str
 
     doc = {'doc' => r}