I recently conducted a workshop about Contributing to Open-Source at first-ever Rubyconf Philippines. In its introductory talk, I spoke about how Aaron Patterson, fixed a 6 year old bug about Optional Arguments, that existed in Rails.
Bug in ruby
Let's try a small program.
1 2class Lab 3 4def day 5puts 'invoked' 6'sunday' 7end 8 9def run 10day = day 11end 12 13end 14 15puts Lab.new.run 16
What do you think would be printed on your terminal when you run the above program.
If you are using ruby 2.1 or below then you will see nothing. Why is that ? That's because of a bug in ruby.
This is bug number 9593 in ruby issue tracker.
In the statement day = day the left hand side variable assignment is stopping the call to method day. So the method day is never invoked.
Another variation of the same bug
1 2class Lab 3 4def day 5puts 'invoked' 6'sunday' 7end 8 9def run( day: day) 10end 11 12end 13 14puts Lab.new.run 15
In this case again the same behavior is exhibited. The method day is never invoked.
How this bug affects Rails community
You might be thinking that I would never write code like that. Why would you have a variable name same as method name.
Well Rails had this bug because rails has code like this.
1 2def has_cached_counter?(reflection = reflection) 3end 4
In this case method reflection never got called and the variable reflection was always assigned nil.
Fixing the bug
So this bug is fixed in ruby 2.2.0. What about the people who are not using ruby 2.2.0.
The simple solution is not to omit the parameter. If we change the above code to
1 2def has_cached_counter?(reflection = reflection()) 3end 4
then we are explicitly invoking the method reflection and the variable reflection will be assigned the output of method reflection.
And this is how Aaron Patterson fixed six years old bug.