The Hack Spectrum

Near the end of an otherwise excellent presentation on the boost shared pointers(boost::shared_ptr), Jonathan showed a slide with the title "Tricks." On this slide it explained how to create a smart pointer to a stack based or static object. This immediately raised by "hack"les.

Pointing a smart pointer at an auto variable violates the semantics of the pointer. The fact that it is syntacticly correct is not an excuse. In fact I consider this a defect in the design of the smart pointer -- a well designed smart pointer would not allow such nonsense. [Note what constitutes a well design smart pointer [IMO] is another topic that I might get into later...]

Jonathan defended the trick by saying "as long as you know what you are doing, it's ok." Alas, that's not correct. A more accurate statement would be: "As long as you and every programer who touches the system either before or after you is aware of all of the implications of this trick, then it's not quite so bad." What makes this hack so insideous is that it doesn't break your code; I breaks mine, months or years later. What's worse, once I find the true cause of the "bug" in my code I have lost confidence in the reliability of smart pointer. This means that every time I use smart pointer I have to consider and either eliminate or allow for the possibility that some programmer will have violated the semantics of the pointer somewhere in the system.

In Jonathan's defense, the technique he described comes straight from Smart Pointer Programming Techniques page on the boost web site. My quibble is not with Jonathan, but with the author(s) of boost::shared_ptr and that web page.

This has made me ruminate for the last few days on the various hacks I have encountered, or in some cases perpetrated over the years I have been developing software. Using the terminology from my early days as a programmer, I realized that there is a spectrum of hacks ranging from a "slimey hack" (one that works but makes you want to wash your mind out with lysol after you read it) to a "righteous hack" (one that makes you step back in awe at its beauty and clarity.)

So I thought I'd document some of these historic hacks and explain where I think they fit on the slime-to-righteous scale. Watch this space...