Metaprogramming custom control structures in C | Hacker News Reader

Metaprogramming custom control structures in C

chiark.greenend.org.uk

60 pointsAndrewDucker9 comments

As someone who had to single-step through this kind of code in gdb, and who had to use the series of fgreps because the cscope is not smart enough to digest these constructs, I can only suggest - weigh the pros and cons before using this technique, especially the fancier parts of it.

(In agreement) It is tough to imagine the mental investment of another if-statement or more setup/teardown exceeding what's required to notice, understand, and debug one of these structures. You get slightly prettier code at a tremendous possible cost.

It feels like making people aware that they can use bazookas to kill butterflies. People are hopefully reasonable, but it can go very wrong.

All that said, cool.

Agreed. I would be very very careful about using this. The headaches it could cause far outweigh the (arguable) benefits.

I think a good rule of thumb is to only use the preprocessor to generate code that you would be comfortable writing yourself. Spaghetti produced by macros is still spaghetti.

The article reminded me of queue.h from BSD (http://www.openbsd.org/cgi-bin/cvsweb/src/sys/sys/queue.h?re...), but those macros expand to readable code.

These macros are nothing compared to what I consider a real abuse of the preprocessor - a whole functional language implemented just by that! Search for "chaos-pp" in this entry (which has plenty of other wonders too!):

http://stackoverflow.com/questions/652788/what-is-the-worst-...

I did something quite similar to this in [1] and [2] some time ago.

[1] https://github.com/Incubaid/crakoon/blob/master/src/arakoon.... [2] https://github.com/Incubaid/crakoon/blob/master/src/arakoon....

Better called, evil control structures. These macros add little value and makes it harder to understand the code.

#define unless(x) if(!(x))

Oh boy--macros!

Just say no to crack, kids, or you'll end up like the Linux kernel.

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