weight classes

weight.rb

class Weight

  def method_missing(method_id)
    return nil if self.class == Weight
    name = method_id.id2name
    result = nil
    if name =~ /^to_(\w+)s$/
      klass = eval $1.capitalize
      result = klass.from_ounces(self.to_ounces)
    elsif name =~ /^in_(\w+)s$/
      klass = eval $1.capitalize
      result = klass.from_ounces(self.to_ounces).value
    end
    result
  end

  def +(value)
    result = nil
    if value.is_a? Weight
      result = new_from_ounces(in_ounces + value.in_ounces)
    else
      result = new_me(self.value + value.to_f)
    end
    result
  end

  def -(value)
    result = nil
    if value.is_a? Weight
      result = new_from_ounces(in_ounces - value.in_ounces)
    else
      result = new_me(self.value - value.to_f)
    end
    result
  end

  def /(value)
    result = nil
    if value.is_a? Weight
      result = new_from_ounces(in_ounces / value.in_ounces)
    else
      result = new_me(self.value / value.to_f)
    end
    result
  end

  def *(value)
    result = nil
    if value.is_a? Weight
      result = new_from_ounces(in_ounces * value.in_ounces)
    else
      result = new_me(self.value * value.to_f)
    end
    result
  end  

  def %(value)
    result = nil
    if value.is_a? Weight
      result = new_from_ounces(in_ounces % value.in_ounces)
    else
      result = new_me(self.value % value.to_f)
    end
    result
  end

  def **(value)
    result = nil
    if value.is_a? Weight
      result = new_from_ounces(in_ounces ** value.in_ounces)
    else
      result = new_me(self.value ** value.to_f)
    end
    result
  end  

  def ==(value)
    result = false
    if value.is_a? Weight
      result = in_ounces == value.in_ounces
    else
      result = self.value == value.to_f
    end
    result
  end

  def <(value)
    result = nil
    if value.is_a? Weight
      result = in_ounces < value.in_ounces
    else
      result = self.value < value.to_f
    end
    result
  end

  def >(value)
    result = nil
    if value.is_a? Weight
      result = in_ounces > value.in_ounces
    else
      result = self.value > value.to_f
    end
    result
  end

  def <=(value)
    result = nil
    if value.is_a? Weight
      result = in_ounces <= value.in_ounces
    else
      result = self.value <= value.to_f
    end
    result
  end

  def >=(value)
    result = nil
    if value.is_a? Weight
      result = in_ounces >= value.in_ounces
    else
      result = self.value >= value.to_f
    end
    result
  end

  def <=>(value)
    result = false
    if value.is_a? Weight
      result = in_ounces <=> value.in_ounces
    else
      result = self.value <=> value
    end
    result
  end

  def to_i
    @value.ceil.to_i
  end

  def to_f
    @value.round(2)
  end

  def to_s
    result = nil
    unless @value > 1.0
      result = to_f.to_s + unit.to_s
    else
      result = to_f.to_s + unit.to_s + 's'
    end
    result
  end

  def coerce(value)
    result = []
    if value.is_a? Weight
      result = [new_from_ounces(value.in_ounces), self]
    else
      result = [new_me(value), self]
    end
  end

  def value
    @value.round(2)
  end

  def value=(value)
    if value.is_a? Weight
      @value = new_from_ounces(value.in_ounces).value
    else
      @value = value.to_f
    end    
  end

  def unit
    @unit
  end

  protected

  def initialize(value)
    @value = value.to_f if value
    @value ||= 0.0
  end

  def unit=(value)
    @unit = value.to_sym
  end

  def new_me(value)
    self.class.new value
  end

  def new_from_ounces(value)
    self.class.from_ounces(value)
  end

end

class Pound < Weight

  def initialize(value)
    super(value)
    self.unit = :lb
  end

  def to_ounces
    self.value * 16.0
  end

  def self.from_ounces(ounces)
    Pound.new(ounces / 16.0)
  end

end

class Ounce < Weight

  def initialize(value)
    super(value)
    self.unit = :oz
  end

  def to_ounces
    self.value
  end

  def self.from_ounces(ounces)
    Ounce.new(ounces)
  end

end

class Kilogram < Weight

  def initialize(value)
    super(value)
    self.unit = :kg
  end

  def to_ounces
    self.value * 35.274
  end

  def self.from_ounces(ounces)
    Kilogram.new(ounces / 35.274)
  end

end