def inspect
      use_dimension
      a = [Utils.num_inspect(@factor), @dim.inspect]
      a << "@name="+@name.inspect if @name
      a << "@expr="+@expr.inspect if @expr
      a << "@offset="+@offset.inspect if @offset
      a << "@dimensionless=true" if @dimensionless
      if @dimension_value && @dimension_value!=1
        a << "@dimension_value="+@dimension_value.inspect
      end
      s = a.join(",")
      "#<#{self.class} #{s}>"
    end
def inspect
      use_dimension
      a = [Utils.num_inspect(@factor), @dim.inspect]
      a << "@name="+@name.inspect if @name
      a << "@expr="+@expr.inspect if @expr
      a << "@offset="+@offset.inspect if @offset
      a << "@dimensionless=true" if @dimensionless
      if @dimension_value && @dimension_value!=1
        a << "@dimension_value="+@dimension_value.inspect
      end
      s = a.join(",")
      "#<#{self.class} #{s}>"
    end
Inspect string.
 @return [String]
 @example
   Phys::Unit["N"].inspect #=> '#<Phys::Unit 1,{"kg"=>1, "m"=>1, "s"=>-2},@expr="newton">'