Two programming tricks you may find interesting

Every one of us have a different path to expertise in programming, which inevitably leads to unique bag of tricks that each programmer have. Free software and open source enables you to find out about the ones you don’t know yet, and you must be a fool not to use that opportunity.

In this short post I’m going to describe two tricks I learned while working on open source projects.

The first one may seem trivial and obvious to those who still remember “Scoping” chapter of their favourite programming book, but to me it was quite enlightening. It’s really simple: in C++ (and other C-like languages, I believe, including C itself) you can use curly braces inside switch case’s to make up separate scopes for them, enabling you to e.g. declare variables with the same name over and over again (and even with different types). That came in handy in one of my student projects.

The second trick is a lot more interesting. I stumbled upon it while reading shooter, a TUI game. Just as the first one, it deals with dispatching, only this time we want to call different functions depending on the message type. Approach is stunning: let’s get rid of switch! To do so, we must:

1. define static array of pointers to functions we want to call; and
2. use message type as an index in the array of pointers.

That, of course, requires message types to be defined in some enumeration, and pointers to functions should be in the same order as the corresponding message types. While the first requirement is true for switch as well, the second one is the main disadvantage of the trick: if order gets out of sync, you’ll get quite tricky bug to find.

Effectively, that’s a vtable.

To see how this trick looks like in the wild, see that array definition and this usage example.

Thanks for reading!