Custom Rails Validation (Reusable Macro Style)

Writing a Rails Application. I would like to make some more commonly used validations available in my models. I understand how to do inline checks, and how to write my own methods. However, I find that I use the same checks in several places, and I'm embarrassed to use mixins for different classes.

Here is an example: I have an object with prop1 and prop2. Any of them is valid, but it is incorrect to set both parameters. Right now, I have something like

class MyClass < ActiveRecord::Base 
  attr_accessor :prop1, :prop2
  validate :prop1_prop2_mutex

  def prop1_prop2_mutex 
     errors.add(:base, "Can not set prop1 and prop2") if prop1 && prop2
  end 
end

What I really like is something like

class MyClass < ActiveRecord::Base 
  attr_accessor :prop1, :prop2
  validate_mutex :prop1, :prop2
end 

and then elsewhere, I guess I need something like

  def validate_mutex(property1, property2)
    rrors.add(:base, "Can not set prop1 and prop2") if self.send(property1) && self.send(property2)
  end

Perhaps this is not so.

So how can I create a new reuse method? Or is there a better way to approach this problem?

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