simplifies +/- methods for durations and ranges

lib/duranged/base.rb

@@ -39,25 +39,13 @@ def <=>(other)
     end
 
     def +(other)
-      if other.is_a?(Duration) || other.is_a?(Interval)
-        Duranged.logger.warn "Warning: You are adding a #{other.class.name} to a #{self.class.name}, which will result in a #{self.class.name}. If you would like a #{other.class.name} object to be returned you must add your #{self.class.name} to your #{other.class.name} instead." if other.is_a?(Range)
-        self.class.new(value + other.value)
-      elsif other.is_a?(Integer)
-        self.class.new(value + other)
-      else
-        raise ArgumentError, "value must be an Integer, Duranged::Duration or Duranged::Interval"
-      end
+      Duranged.logger.warn "Warning: You are adding a #{other.class.name} to a #{self.class.name}, which will result in a #{self.class.name}. If you would like a #{other.class.name} object to be returned you must add your #{self.class.name} to your #{other.class.name} instead." if other.is_a?(Range)
+      self.class.new(to_i + other.to_i)
     end
 
     def -(other)
-      if other.is_a?(Duration) || other.is_a?(Interval)
-        Duranged.logger.warn "Warning: You are subtracting a #{other.class.name} from a #{self.class.name}, which will result in a #{self.class.name}. If you would like a #{other.class.name} object to be returned you must subtract your #{self.class.name} from your #{other.class.name} instead." if other.is_a?(Range)
-        self.class.new(value - other.value)
-      elsif other.is_a?(Integer)
-        self.class.new(value - other)
-      else
-        raise ArgumentError, "value must be an Integer, Duranged::Duration or Duranged::Interval"
-      end
+      Duranged.logger.warn "Warning: You are subtracting a #{other.class.name} from a #{self.class.name}, which will result in a #{self.class.name}. If you would like a #{other.class.name} object to be returned you must subtract your #{self.class.name} from your #{other.class.name} instead." if other.is_a?(Range)
+      self.class.new(to_i - other.to_i)
     end
 
     protected

lib/duranged/range.rb

@@ -49,23 +49,11 @@ def end_at(format=nil)
     alias_method :end_time, :end_at
 
     def +(other)
-      if other.is_a?(Duration) || other.is_a?(Interval)
-        self.class.new(start_at, value + other.value)
-      elsif other.is_a?(Integer)
-        self.class.new(start_at, value + other)
-      else
-        raise ArgumentError, "value must be an Integer, Duranged::Duration or Duranged::Interval"
-      end
+      self.class.new(start_at, to_i + other.to_i)
     end
 
     def -(other)
-      if other.is_a?(Duration) || other.is_a?(Interval)
-        self.class.new(start_at, value - other.value)
-      elsif other.is_a?(Integer)
-        self.class.new(start_at, value - other)
-      else
-        raise ArgumentError, "value must be an Integer, Duranged::Duration or Duranged::Interval"
-      end
+      self.class.new(start_at, to_i - other.to_i)
     end
 
     def to_duration