Question

I’m trying to retrieve the tax rate based on the timestamp. It doesn’t make sense to me to do a simple mixin where I define “tax_rate” in the Time class. It makes more sense to put “tax_rate” in a “Government” class (or module? I don’t know I’m new to this) and simply have the method be available to the Time class with an option to assume the current time if used on its own.

examples:

Time.now.tax_rate == 0.13
10.years_ago.tax_rate == 0.10
Government.tax_rate == 0.13 (assumes Time.now)

Where the method tax_rate is as follows:

def self.tax_rate
  t = self || Time.now # I know this part won't work properly, I'll fix it later. I want it to default to using the current Time object or if the method is used on its own, the current time.
  return 0.10 if t < Time.parse("July 1, 2001")
  return 0.12 if t < Time.parse("July 1, 2010")
  0.13
end

I basically need to reference tax rates in different classes in my rails project and I feel that putting it straight into one of the models just doesn’t fit right. It needs to be on its own.

Answer 1

Why not just have a TaxRate module?

module TaxRate
  def self.get t = Time.now
    t = Time.parse(t) if t.kind_of?(String)
    case
    when t < Time.parse("July 1, 2001") then 0.10
    when t < Time.parse("July 1, 2010") then 0.12
    else 0.13
    end
  end
end

TaxRate.get #=> 0.13
TaxRate.get(Time.now) #=> 0.13
TaxRate.get("July 1, 2000") #=> 0.10
TaxRate.get("July 1, 2012") #=> 0.13
TaxRate.get(10.years_ago) #=> 1.10

If you want to define tax_rate on Time, which I think is unnatural, then, just monkey patch Time.

class Time
  def tax_rate
    case
    when self < Time.parse("July 1, 2001") then 0.10
    when self < Time.parse("July 1, 2010") then 0.12
    else 0.13
    end
  end
end

Time.now.tax_rate #=> 0.13
10.years_ago.tax_rate #=> 0.10