app/validators/width_validator.rb

   1 class WidthValidator < ActiveModel::Validations::LengthValidator
   2   module WidthAsLength
   3     def length
   4       Unicode::DisplayWidth.of(to_s)
   5     end
   6   end
   7
   8   def validate_each(record, attribute, value)
   9     super(record, attribute, value.extend(WidthAsLength))
  10   end
  11 end