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.
> 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)
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