Re: [boost] [proto] design of expr<>

From: Larry Evans (cppljevans_at_[hidden])
Date: 2008-03-22 07:40:04

On 03/22/08 06:12, Dean Michael Berris wrote:
[snip]
> I think this begs the question then, what is the necessity for an
> Arity parameter as part of the definition of an expr<>?
> 

According to:

http://archives.free.net.ph/message/20080310.170830.c4548dd4.en.html

it's use for specialization.  In my reply to that post I suggested
maybe a helper template to eliminate the need for this 3ird
parameter, but then, AFAICT, this just delays the need for a 3
parameter expr...but wait, if some how the 2 parameter expr
were public and somehow the 3 parameter were made private,
maybe that would be better.  Like you, I'm just "throwing
some ideas around".  Apparently it's not used to enforce
the arity of the 2nd expr arg.  Eric suggested this
be done by using a grammar and matches, but AFAICT that
sorta delays the detection of arity violation.