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

Subject: Re: [boost] Review Request: Variadic Macro Data library
From: Edward Diener (eldiener_at_[hidden])
Date: 2011-02-21 09:19:42

On 2/21/2011 4:05 AM, Paul Mensonides wrote:
> 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

Thanks ! I will just have to further document that the data size 
returned can never be 0, even when the variadic macro is invoked with 
an empty argument.

>
> This is yet another reason why variadic content doesn't make for a good
> data structure.

Agreed.

>  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)