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

Just to clarify more, we need to add classes to be extended in core_ext.rb . file :
1) Create core_ext.rb file under config\initializers folder in your project.
2) Paste below as mentioned by @songyy in his answer:

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

Reference:
https://guides.rubyonrails.org/plugins.html#extending-core-classes