output.diff

diff --git a/lib/strscan.rb b/lib/strscan.rb
index c7c2b97..78dcb41 100644
--- a/lib/strscan.rb
+++ b/lib/strscan.rb
@@ -46,7 +46,7 @@ class StringScanner
   end
 
   def concat(str)
-    @string << str
+    @string << StringValue(str)
     self
   end
   alias_method :<<, :concat
@@ -78,7 +78,7 @@ class StringScanner
   end
 
   def initialize(string, dup=false)
-    @string = String.new(string)
+    @string = StringValue(string)
     reset_state
   end
 
@@ -146,7 +146,7 @@ class StringScanner
   end
 
   def pre_match
-    @string.substring(0, match.begin(0)) if @match
+    @string.substring(0, match.begin(0)).to_str if @match
   end
 
   def reset_state
@@ -161,7 +161,7 @@ class StringScanner
   end
 
   def rest
-    @string[pos..-1]
+    @string[pos..-1].to_str
   end
 
   def rest?
@@ -207,7 +207,7 @@ class StringScanner
 
   def string=(s)
     reset_state
-    @string = s
+    @string = StringValue(s)
   end
 
   def terminate
@@ -229,7 +229,7 @@ class StringScanner
     return "" if len.zero?
 
     begin
-      return @string[pos, len]
+      return @string[pos, len].to_str
     rescue TypeError
       raise RangeError, "offset outside of possible range"
     end
@@ -271,7 +271,7 @@ class StringScanner
 
     return width unless getstr
 
-    @string.substring(@prev_pos, width)
+    @string.substring(@prev_pos, width).to_str
   end
   private :_scan
 end