Class ActiveModel::Validations::WithValidator < EachValidator

    # File activemodel/lib/active_model/validations/with.rb, line 12
12:       def validate_each(record, attr, val)
13:         method_name = options[:with]
14: 
15:         if record.method(method_name).arity == 0
16:           record.send method_name
17:         else
18:           record.send method_name, attr
19:         end
20:       end