Thursday 20 February 2014

Trust, Safety, Sandi Metz and A Proverb Walked Into A Bar...

Rereading POODR again. I love the bit in Chapter 6 where she talks about using a post_initialize method to decouple subclasses from having to remember to call super in an initialize method override. That's the sort of thing I remember making work in UCSD Pascal back when it wanted to be the Next Hot Language™, and in a few languages since.

But one question I never found an acceptable answer to was, how do I prevent myself from forgetting to call super (or its equivalent) in a hierarchy with multiple levels? Sure, the base class implements a do-nothing post_initialize-type method, so that every single subclass anywhere in the hierarchy can "kick it upstairs" and things will Just Work.

But at some point, you have to trust yourself, your team, your successors who grapple with your code long after you are gone. Comprehensive tests will catch the fallout from a forgotten upstairs kick and give you a lovely red bar — or will show you that the parent's chained behaviour you thought you needed was either frivolous or incorrectly verified. (Or both. Shtuff happens; nobody ever went broke underestimating the degree to which developers can fool ourselves.) Whatever twisty little maze of keystrokes leads to you that point, you've discovered a refactoring opportunity. Enjoy your Homer Simpson Moment, make the appropriate changes, verify that the tests still pass, and move on.

Доверяй, но проверяй.

No comments: