Re: [boost] Review Request: Variadic Macro Data library

Subject: Re: [boost] Review Request: Variadic Macro Data library
From: Paul Mensonides (pmenso57_at_[hidden])
Date: 2011-02-21 04:05:22

On Sun, 20 Feb 2011 20:25:43 -0500, Edward Diener wrote:

> I think Paul Mensonides may be right and there is no foolproof way to
> check for a completely empty parameter list even using variadic macros.
> Further ideas ?

Trust me, I am right.  About the best you can do is prohibit input that 
terminates in a function-like macro name.  You can generally detect 
emptiness *except* for that case.

However, DATA_SIZE() => 0 is ill-conceived.  An empty argument is still 
an argument to the preprocessor.  A better correlation is:

DATA_SIZE(,,) => 3
DATA_SIZE(,) => 2
DATA_SIZE() => 1

This is yet another reason why variadic content doesn't make for a good 
data structure.  There is no way to denote the empty sequence.  For all 
others, there are ways:

(,,) // 3-element tuple
(,)  // 2-element tuple
()   // 1-element tuple
     // 0-element tuple (blank)

()()() // 3-element seq
()()   // 2-element seq
()     // 1-element seq
       // 0-element seq (blank)

Regards,
Paul Mensonides