[boost] [tuple] can't get size of const empty null tuple.

From: Giovanni P. Deretta (gpderetta_at_[hidden])
Date: 2006-05-22 12:11:35

Hi all,

With GCC 3.4.6, when compiling this simple program,

(in tuple_test.cc)
  1: #include <boost/tuple/tuple.hpp>
  2: typedef const boost::tuple<> tuple;
  3: const int size  = boost::tuples::length<tuple>::value;
  4: int main() {}

I get
  /usr/local/include/boost/tuple/detail/tuple_basic.hpp: In 
instantiation  of `boost::tuples::length<const tuple>':
  tuple_test.cc:3:   instantiated from here
/usr/local/include/boost/tuple/detail/tuple_basic.hpp:483: error: no 
type named `tail_type' in `const class tuple'

If i remove "const" from line 2, the program compiles fine.
It also compiles if line 2 is substituted with:
  "typedef const boost::tuple<int> tuple;"

I think that 'length' not working with const empty tuples is clearly a 
bug. Shouldn't 'boost::tuples::length' need to be specialized for 'const 
tuple<>' in addition to 'tuple<>'?

-- 
Giovanni P. Deretta