Hashmaps are not simple

(written by lawrence krubner, however indented passages are often quotes). You can contact lawrence at: lawrence@krubner.com


I was at this talk and I disagree with his fundamental statement that simple + simple = simple. I program in Ruby one of the biggest problems beginners make is not creating complex data structures where they are needed. Instead they pass around hashes of hashes of hashes. Why? Hashes are simple, they’re easy to understand and work with. Unfortunately this initial simplicity introduces unexpected complexity, things like deep dup and deep merge are now needed. Every part of your system must now know the hash structure you’re using and often reproduce logic in many places like dealing with optional keys that may be missing. By not isolating the complexity to one part of the app it must now be shared by the entire app. simple + simple !(always)= simple.

If I had a time machine and could make one change in an open source project it would be to go back and remove the design choice of putting using hashes as internal config objects in Rails. It makes understanding all the possible edge cases almost impossible unless you’re really familiar with the project.

The second is the claim of speed that this “simplicity” buys you. I agree that functional programming is extremely fast when it’s parallelized and it’s extremely easy to make a functional program parallelizable. When we’re dealing with sequential tasks, mutating data is much faster than allocating new data structures. I think clojure helps with the speed of allocating new immutable structures by using copy on write strategies behind the scenes.