Re: [Boost-users] [tr1] maximum number of allowed tuple elements?

From: John Maddock (john_at_[hidden])
Date: 2008-08-25 08:33:59

Markus Werle wrote:
> Then it would be very nice if the standard defined a MACRO allowing
> me to determine the maximum number of tuple elements.
> Otherwise this renders tr1::tuple completely useless for any template
> code.

Really?  I've never actually needed more than about 3 elements myself.  In 
any case the next std will have variadic template support which will allow 
for an infinite (ish) number of arguments to std::tuple.

>> So you can't change it, or portably store more than 10 elements.  Of
>> course if you just happen to be using the Boost implementation then
>> all the Boost.Fusion macros and extensions kick in, but you can't
>> guarentee that: to take one example VC9+sp1 supplies it's own TR1
>> tuple so that's what Boost.TR1 pulls in (out of necessity).
>
> Yes. I was aiming at getting std::portable ...
> These "implementation defined" clauses suck (not only IMHO).
> It is like those "maximum nesting level of 18 in templates" that
> hinders portability for RealWorld apps.
>
> Thinking about variadic template arguments while releasing a TR that
> clings to fixed numbers seems odd to me ...

The TR is aimed at *existing* compilers, it introduces no language changes, 
the next std will have a tuple with variadic argument support.

HTH, John.