module ActiveModel::Validations::Callbacks::ClassMethods

person.name # => "bob"
person.valid? # => true
person.name = ' bob '
person = Person.new

end
end
name.strip!
def remove_whitespaces

private

before_validation :remove_whitespaces

validates_length_of :name, maximum: 6

attr_accessor :name

include ActiveModel::Validations::Callbacks
include ActiveModel::Validations
class Person

Defines a callback that will get called right before validation.

def before_validation(*args, &block)
  options = args.last
  if options.is_a?(Hash) && options[:on]
    options[:if] = Array(options[:if])
    options[:on] = Array(options[:on])
    options[:if].unshift ->(o) {
      options[:on].include? o.validation_context
    }
  end
  set_callback(:validation, :before, *args, &block)
end