Method: RubyUnits::Unit#-

Defined in:

lib/ruby_units/unit.rb

#-(other) ⇒ Unit

Subtract two units. Result is same units as receiver and scalar and base_scalar are updated appropriately

Parameters:

• other (Numeric)

Returns:

• (Unit)

Raises:

• (ArgumentError) —

  when subtracting a temperature from a degree

• (ArgumentError) —

  when units are not compatible

• (ArgumentError) —

  when subtracting a fixed time from a time span

# File 'lib/ruby_units/unit.rb', line 741

def -(other)
  case other
    when Unit
      case
        when self.zero?
          if other.zero?
            other.dup * -1 # preserve Units class
          else
            -other.dup
          end
        when self =~ other
          case
            when [self, other].all? { |x| x.is_temperature? }
              RubyUnits::Unit.new(:scalar => (self.base_scalar - other.base_scalar), :numerator => KELVIN, :denominator => UNITY_ARRAY, :signature => @signature).convert_to(self.temperature_scale)
            when self.is_temperature?
              RubyUnits::Unit.new(:scalar => (self.base_scalar - other.base_scalar), :numerator => ['<tempK>'], :denominator => UNITY_ARRAY, :signature => @signature).convert_to(self)
            when other.is_temperature?
              raise ArgumentError, "Cannot subtract a temperature from a differential degree unit"
            else
              @q ||= ((@@cached_units[self.units].scalar / @@cached_units[self.units].base_scalar) rescue (self.units.unit.scalar/self.units.unit.to_base.scalar))
              RubyUnits::Unit.new(:scalar => (self.base_scalar - other.base_scalar)*@q, :numerator => @numerator, :denominator => @denominator, :signature => @signature)
          end
        else
          raise ArgumentError, "Incompatible Units ('#{self}' not compatible with '#{other}')"
      end
    when Time
      raise ArgumentError, "Date and Time objects represent fixed points in time and cannot be subtracted from to a Unit, which can only represent time spans"
    else
      x, y = coerce(other)
      return y-x
  end
end