[boost] [fusion] make_fused arity > 10

Subject: [boost] [fusion] make_fused arity > 10
From: Mario Mulansky (mario.mulansky_at_[hidden])
Date: 2011-07-20 11:22:51

Hi

We are using Boost.Fusion quite heavily in our library [odeint] and I just came across some problem that took me several hours to solve so I decided to let you know about the issue.
We use boost::fusion::make_fused to make functor applicable to fusion sequences and as we occasionally deal with long vectors we increased the limits as described here:
http://www.boost.org/doc/libs/1_47_0/libs/fusion/doc/html/fusion/functional/adapters/limits.html
At first we used 10 as maximum (also changing FUSION_MAX_VECTOR_SIZE and the ..INVOKE.. constants, of course). However, today I extended the library and had to increase these values to 16. Unfortunately, that did not work - compiling still failed at functors with arity 11. So I digged into Boost.Fusion and after quite some time I realized that it relies on boost::result_of which has an upper limit of 10. So additionally changing BOOST_RESULT_OF_NUM_ARGS to 16 made everything work, eventually.

I think the point here is that defining BOOST_FUSION_UNFUSED_MAX_ARITY > 10 without also defining BOOST_RESULT_OF_NUM_ARGS accordingly will break the code in a rather confusing way - I think at least adding a note in the docs could be very helpful here.

Regards, 
Mario