In an equally named article, the excellent (yes. Really. This is one of the blogs you HAVE to subscribe to) Coding Horror blog talks about flattening out deeply stacked IF-clauses in your code.
I so agree with the guy, though there seem to be two opinions in the matter of the points 1 and 4 in the list the article provides:
Replace conditions with guard clauses. This code..
Many people disagree. Sometimes because they say that Exceptions are a bad thing (I don’t get that either) and sometimes because they says that a function should only have one return point
Always opportunistically return as soon as possible from the function. Once your work is done, get the heck out of there! This isn’t always possible — you might have resources you need to clean up. But whatever you do, you have to abandon the ill-conceived idea that there should only be one exit point at the bottom of the function.
I once had to work with code a intern has written for us. It was exactly written as Coding Horror tells you not to. It was PHP code and all of it basically took place in a biiig else-clause around the whole page, with a structure like this:
if (!$authenticated){
die('not authenticated');
else{
// 1000 more lines of code, equally structured
}
This is a pain to read, understand and modify.
To read because the thing get’s incrediby wide requiring you to scroll horizontally, to understand because you sometimes find an }else{ not having the slightest idea where it belongs to, requiring you to scroll upwards for half a file to see the condition and to modify because PHP’s parser is inherently bad at reporting the exact position missing or spurious braces, which is bound to happen when you extend the beast.
But back to the quote: I talked to that intern about his code style (there were other things) and he mostly agreed, but he refused to change those deeply stacked IF’s. “A function must only have one single point of return. Everything else is bad design“, he told me.
Point is. I kinda agree. Multiple exit points can make it hard to understand the workings of a function. But if it’s a single, well definded condition that makes the function unable to continue or if the function somehow gets its result way early (like if it’s able to read the data from a cache of some kind), IMHO there’s nothing wrong with just stopping to work. That’s easy to read and understand and certianly does not have above problems.
And of course every function should be short enough to fit on one screen, so scrolling is never neccessary and it’s always obvious where that }else{ belongs to – at least without making you scroll.
Personally, I write code exactly as it is suggested in that article. And I try to keep my functions short. Like this, it’s very easy to understand the code (most of the time) and thus to extend it. Even by third parties.
Christoph, do you agree? And: No, I’m not talking about that sort-by-material-group-thing. That IS unclean. I know that (and so do you now *evilgrin*)
gnegg 