Are there more elegant ways to prevent negative numbers in Ruby?

Question

Given that I\'d like to do the following calculation:

total = subtotal - discount

Because discount might be greater than

Answer 1

Thinking we can extend the Numeric class?

class Numeric                                                                  
  def non_negative                                                             
    self > 0 ? self : 0                                                                      
  end                                                                          
end                                                                            

class Calculator
  def initialize(subtotal: subtotal, discount: discount)
    @subtotal = subtotal
    @discount = discount
  end

  def total
    (@subtotal - @discount).non_negative
  end
end