🚀 go-pugleaf

Mark Russell (M.T.Russell@ukc.ac.uk) wrote:

> Here's an idea I had for a non-preprocessor replacement for #if and  #ifdef.
> 	if const (<expr>) { <stuff> }

> `if const' is a compile time version of `if'.  <expr> is a constant
> expression which is convertible to bool.  If it yields true, <stuff>
> is processed as normal.  Otherwise <stuff> is parsed into tokens, but
> ignored except for counting { and } nesting.  <stuff> is anything that
> can appear inside a namespace block.  `if const' does not introduce a
> new scope.

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 */
   }

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).

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.

On the other hand, I'd really like to see function-like macros eased out
of usage..
--
Shankar Unni				E-Mail:	shankar@sgi.com
Silicon Graphics Inc.			Phone:	+1-415-933-2072
URL:	http://reality.sgi.com/employees/shankar


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