Re: [boost] Re: Debug mode

From: Gregory Seidman (gseidman_at_[hidden])
Date: 2001-01-23 11:34:42

Dean Sturtevant sez:
} --- In boost_at_[hidden], Gregory Seidman <gseidman_at_a...> wrote:
} > Why not just use #ifndef NDEBUG? It keeps things consistent with
} > cassert and, like cassert, allows automatic building of debugging and
} > optimized versions. Of course, with any system we devise it is possible
} > for the end programmer to put the #ifndef NDEBUG in his own code, but
} > much of the point of boost is to make less work for the programmer.
} > 
} > What is the win of a scheme other than NDEBUG?
} > 
} As with anything, there are tradeoffs. If it was up to me, I'd do 
} what you suggested. But when I introduced the idea of putting asserts 
} in boost (last month?), some people objected on the basis that 
} the 'one definition rule' (ODR) would be violated. They were 
} concerned that modules compiled with different settings of NDEBUG 
} might be linked together in the same program. In order to accommodate 
} them, I proposed using a different namespace (boost_debug) to put 
} assert-laden code in. This has the drawback that one then needs a 
} macro to establish the boost namespace, but it does avoid ODR 
} violations. In fact, this is the technique the STLPort uses.

Okay, try this on for size. We have two namespaces: boost_debug and
boost_optimized (or whatever... bear with me). Each boost header looks
something like this:

#ifndef BOOST_THISFUNCTIONALITY_HPP
#define BOOST_THISFUNCTIONALITY_HPP

#ifndef NDEBUG
//the code in this file is contained in namespace boost_debug;
#include <boost/thisfunctionality_debug.hpp>
#else
//the code in this file is contained in namespace boost_optimized
#include <boost/thisfunctionality_optimized.hpp>
#endif

namespace boost {
#ifndef NDEBUG
  using namespace boost_debug;
#else
  using namespace boost_optimized;
#endif
}

#endif //BOOST_THISFUNCTIONALITY_HPP

Now, the debug stuff is in a separate namespace from the ordinary or
optimized version, so linking between debugging and non-debugging objects
will fail outright. Nonetheless, the programmer simply uses boost:: (or
using namespace boost) to access whichever version (which will be drawn
into the boost namespace), but the version is chosen at compile-time with
(or without) -DNDEBUG. Note that the includes in the middle could just be
the appropriate definitions in the appropriate namespace; I showed it as
includes for simplicity and readability.

We preserve ODR while preserving ease of use. Any objections?

} - Dean
--Greg