🚀 go-pugleaf

shankar@mti.mti.sgi.com (Shankar Unni) writes:

>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 */
>   }

But with `if const', your 11 lines of code could be rewritten as either

	if (some condition) {
		if (SOMEIMPL && some other condition) {
			/* code */
			/* code */
			/* code */
		}
	}

	(7 lines of code)

or, if `some other condition' won't compile on other implementations, as

	if (some condition) {
		bool some_other_condition = true;
		if const (SOMEIMPL) {
			some_other_condition = some other condition;
		}
		if (other_condition) {
			/* code */
			/* code */
			/* code */
		}
	}

	(11 lines of code)

Both of these solutions have the advantage that the test for `SOMEIMPL'
occurs only once, so things will be easier if you later have to change it to 
`SOMEIMPL || SOMEOTHERIMPL'.

>Duplicating all the code so that each half is precisely correct in its {}
>matching is both tedious and error-prone (trying to verify that both parts
>of the expression are fixed).

But fortunately as shown above it would not be required.

>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.

True, but a convention of using upper-case for SOMEIMPL and similar constants
would make such tests stand out.

--
Fergus Henderson             	WWW: http://www.cs.mu.oz.au/~fjh
fjh@cs.mu.oz.au              	PGP: finger fjh@128.250.37.3
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