lib/periodical/period.rb in periodical-1.1.0 vs lib/periodical/period.rb in periodical-1.2.0

@@ -34,28 +34,30 @@
 				self.unit.to_s
 			end
 		end
 		
 		def advance(date, multiple = 1)
+			raise TypeError unless date.is_a?(Date)
+			
 			self.send("advance_#{unit}", date, multiple * self.count)
 		end
 		
 		private
 		
 		def advance_days(date, count)
 			date + count
 		end
 		
 		def advance_weeks(date, count)
-			date + (7 * count)
+			advance_days(date, count*7)
 		end
 		
 		def advance_months(date, count)
 			date >> count
 		end
 		
 		def advance_years(date, count)
-			date >> (12 * count)
+			advance_months(date, count*12)
 		end
 		
 		class << self
 			# Accepts strings in the format of "2 weeks" or "weeks"
 			def parse(string)