Why we need try…finally, not just RAII

The claim has been made that because C++ supports RAII (resource acquisition is initialization), it doesn’t need try…finally. I think this is wrong. There is at least one use case for try…finally that’s very awkward to model with RAII, and one that’s so ugly it ought to be outlawed.

The awkward use case

What if what you want to do during a …finally block has nothing to do with freeing resources? For example, suppose you’re writing the next version of Guitar Hero, and you want to guarantee that when your avatar leaves the stage, the last thing she does is take a bow–even if the player interrupts the performance or an error occurs.

…finally, take a bow. Photo credit: gavinzac (Flickr)

Of course you can ensure this behavior with an RAII pattern, but it’s silly and artificial. Which of the following two snippets is cleaner and better expresses intent? Continue reading

Headers, babies, and bathwater

I claim that by eliminating the C/C++-style dichotomy between headers and implementation, most modern programming languages have thrown out the baby with the bathwater.

Don't throw out the baby with the bathwater! Photo credit: StubbyFingers (Flickr)

Don’t throw out the baby with the bathwater! Photo credit: StubbyFingers (Flickr)

If that sounds crazy, just hang with me for a minute.

I know my claim runs counter to popular wisdom; have a look at this thread on stackoverflow.com. Designers of languages like python and go and D and ruby and java consider it a feature that developers don’t have two redundant pictures of the same functionality. This comment from the C# 5.0 specification is typical:

“Because an assembly is a self-describing unit of functionality containing both code and metadata, there is no need for #include directives and header files in C#. The public types and members contained in a particular assembly are made available in a C# program simply by referencing that assembly when compiling the program” (p 3).

I agree.

Sort of…

Bad headers are a royal pain

It can be onerous to maintain the parallelism between a .h and a .cpp. And most C/C++ headers are managed so poorly that the benefits you might claim for them are theoretical rather than real. Three common antipatterns that I particularly detest: Continue reading