[boost] Re: Meta programming 'debug' mode.

From: Dirk Gerrits (dirk_at_[hidden])
Date: 2003-03-09 15:45:03

Dirk Gerrits wrote:
 > Jaap Suter wrote:
 >
 >> Hi,
 >>
 >> In my own meta-programming I tend to use a lot of static_asserts and
 >> concept
 >> checks. However, these do have a negative impact on my compile-times.
 >> Take,
 >> for example, a meta-function that takes a type-list as its parameter.
 >> Assume
 >> a pre-condition is that the list may not be empty. What I can do is:
 >>
 >> BOOST_STATIC_ASSERT( (mpl::not_< typename mpl::empty< List >::type
 >>
 >>> ::type::value) );
 >>
 >>
 >>
 >> And while this is a good thing most of the time, sometimes I would
 >> like to
 >> disable these checks so my compiles go faster. What is the recommended
 >> way
 >> of doing this?
 >>
 >> 1. Using a define:
 >>
 >> #ifndef UID_DO_CHECKS
 >>     BOOST_STATIC_ASSERT( (mpl::not_< typename mpl::empty< List >::type
 >>
 >>> ::type::value) );
 >>
 >>
 >> #endif
 >>
 >> 2. Using a boolean trait or policy, that is passed to a meta-if
 >> statement:
 >>
 >> BOOST_STATIC_ASSERT( (
 >>     mpl::apply_if< check_policy,
 >>         mpl::not_< typename mpl::empty< List >::type >::type::value,
 >>         true_ >::type::value ));
 >>
 >> 3. Other ideas?
 >
 >
 > I'd say something like:
 >
 > #ifdef STATIC_NDEBUG
 > #    define BOOST_STATIC_ASSERT2(e) BOOST_STATIC_ASSERT(e)
 > #else
 > #    define BOOST_STATIC_ASSERT2(e) (void(e))
 > #endif
 >
 > Analogous to <cassert>.

Argh, the if and else branches should be reversed of course. You've 
gotta love negative logic. ;)

Dirk Gerrits