On Fri, Aug 17, 2012 at 9:11 PM, Gabriel Dos Reis <g...@integrable-solutions.net> wrote: > On Fri, Aug 17, 2012 at 1:03 PM, Mike Stump <mikest...@comcast.net> wrote: >> On Aug 17, 2012, at 6:58 AM, Paolo Carlini wrote: >>> On 08/17/2012 01:26 PM, Richard Guenther wrote: >>>> This gets rid of this field, pushing it into a short int in tree_base >>>> (hopefully 2^16 non-defaulted template args are enough ...). >>> Honestly, I don't think it's a trivial issue. >> >> Love to hear from Jason, but, my take would be 2^16 should be enough for >> anyone. I think long before people hit that limit, they would merely >> aggregate arguments into classes and structures. I think in another 20-80 >> years, we might want to bump it back up to 32 bits, but... I think we can >> safely wait until we get a compelling bug report for it. > > C++11 says that an implementation should be able to handle at least 2^10 > template parameters, 2^12 members declared in a single class. I believe > that even for automatically generated programs, 2^16 is a good limit. I > suspect > that by the time that limit is a hindrance, C++ would have gone through > several > iterations and more importantly 128-bit integers would be common place, so > by that time we would have plenty of spare bits -- if we haven't already > restructured the tree data structures to use idiomatic C++ constructs that > are both more space and time efficient. > > This is a very long of saying "I am comfortable with the 2^16 restriction > on the number of template parameters. The patch needs to document > that in the usual .texi file."
I searched for a place where we document GNU C++ implmenetation defined behavior / limits but didn't find it. Can you point me to the place where we document that the current limit is 2^31 - 1 _non defaulted_ template parameters? (It looks to me this whole non-defaulted-template-args stuff was just invented to avoid pretty-printing defaulted args, so it does not in any way present an implementation limit but only a possible bug in that we'd never pretty-print more than 2^31 - 1 non-defaulted template paramters in a diagnostic, but who wants to see 2^31 template parameters in a diagnostic anyways ...) Richard. > -- Gaby
