Tuesday, 25 March 2014

Accidental and essential complexity

Response to: http://250bpm.com/blog:36

This sort of reminds me of Rodney Brook's commentary on essential and accidental complexity. Once you have got rid of the accidental complexity, you are left with the essential complexity, which cannot be further reduced without compromising on functionality.

You can shovel the essential complexity around your system design all you like, but the overall quantity of complexity still remains constant. A practical consequence of this is that you can move the complexity away from the 1500 line function by splitting it up into smaller functions, but that complexity remains embedded in the implicit relationship that exists between all of your 50 line functions. (Plus some additional overhead from the function declarations themselves).

Of course, splitting up the large function into smaller ones gives you other benefits: Primarily the ability to test each small function in isolation, but also (and more importantly) the ability to read and understand the scope and purpose of each small function without being confused by irrelevant details.

Personally, I would like to have the ability to give names to chunks of code within a large function - and to write tests for those chunks without having to extract them into separate smaller functions.

I would also like to see better tools (and widespread usage of those that exist) for building various graphs and diagrams showing the call-graph and other relationships between functions and objects, so that we can explore, understand, and communicate the implicit complexity encoded in program structure more easily.