add File.path

mrblib/file.rb

@@ -170,4 +170,14 @@ class File < IO
     ext = fname.split('.').last
     ext.empty? ? '' : ".#{ext}"
   end
+
+  def self.path(filename)
+    if filename.kind_of?(String)
+      filename
+    elsif filename.respond_to?(:to_path)
+      filename.to_path
+    else
+      raise TypeError, "no implicit conversion of #{filename.class} into String"
+    end
+  end
 end