On 11/13/2011 9:48 PM, Gennadiy Rozental wrote:
Edward Diener<eldiener<at> tropicsoft.com> writes:
the page. My comment is:
"#define AMACRO(x) () IS_EMPTY(AMACRO) is true, where of course it should be false.
Are you sure? My gcc (cygwin) says it false.
I admit I do not understand how this can be. in the expansion to the code on that page it sure looks to me like 'HAS_COMMA(_TRIGGER_PARENTHESIS_ __VA_ARGS__ (~))' will equate to 1 when __VA_ARGS__ = AMACRO since 'AMACRO (~)' = '()', '_TRIGGER_PARENTHESIS_ ()' = ',', and HAS_COMMA(,) = 1. I will look at it in Wave, which I trust more than most anything as a preprocessor.
On the other hand if you define it like this:
#define AMACRO(x,y) anything here
if fails to build.
In any case, as I said previous, this is corner case we should just document, but size should return zero when we actually did not pass any arguments to the macro.
I did document this corner case in my VMD but clearly it makes an IS_EMPTY macro not 100% reliable, as it makes your solution not 100% reliable. It is no use saying that you have a foolproof solution to size returning 0, when it is clearly not foolproof. OTOH I personally am not against having a solution that is not 100% reliable else I would not have put out the latest version of VMD. But, although I can not speak for him, I have a strong impression that Paul does not want such code in Boost PP.