🚀 go-pugleaf

Shankar Unni (shankar@engr.sgi.com) wrote:
>No dice.
>
>Often, an #ifdef covers just a small part of an expression that may be
>different between different environments, or some such small differences:
>
>   if (some condition) {
>#ifdef SOMEIMPL
>	if (some other condition) {
>#endif /* SOMEIMPL */
>	/* code */
>	/* code */
>	/* code */
>#ifdef SOMEIMPL
>	}
>#endif /* SOMEIMPL */
>   }

Personally I would be quite happy to see that style of #ifdef'ing
disappear.  I've seen too much code rendered totally impenetrable by
just this technique.  I would write the above as:

	if (some condition) {
		if const (SOMEIMPL) {
			if (some other condition)
				code();
		}
		else const {
			code();
		}
	}

where code() is the code wrapped up in a (possibly inline) function.
Alternatively, if you can persuade your compiler not to complain about
a constant if() controlling expression:

	if (some condition) {
		bool doit;

		if const (SOMEIMPL) {
			doit = some other condition;
		}
		else const {
			doit = true;
		}

		if (doit) {
			code
		}
	}

Of course in reality you would hope to bury all the implementation
dependent stuff behind a portability layer.

>Also, the #ifdefs serve a purpose in pointing out the fact that this piece
>of code is system-dependent.  The syntax you propose hides its warts rather
>too well, and make it easy for a reader to miss the significant piece of
>information that this area of code is system-dependent.

I agree that this is a problem, but I would argue that sprinkling `if
const' (or #ifdef) throughout the main body of the code is bad style,
and thus comes under the `any feature can be misused' getout.  Misuse
like this is easily spotted: `if const' is just as visible to grep as #if.

Mark

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