BOOST_STATIC_ASSERT_MSG

From: John Maddock (John_Maddock_at_[hidden])
Date: 2001-11-26 07:58:41

I've had a go at producing a version of BOOST_STATIC_ASSERT that produces a
user defined message in compiler error output, but which meets the same
requirements as BOOST_STATIC_ASSERT: that is that it produces neither code
nor data, and is usable at class, function or namespace scope.

here's the first attempt:

#define BOOST_STATIC_ASSERT_MSG(cond,msg) \
   struct BOOST_JOIN(_,msg){ ::boost::STATIC_ASSERTION_FAILURE<(cond)> msg;
};\
   typedef int BOOST_JOIN(msg,_typedef)[sizeof(BOOST_JOIN(_,msg))]

There is also a test program attached so you can see what kind of messages
it produces (you will need to uncomment one of the lines following an //
errror: comment).  The typedef part of the implementation above is required
for g++ which doesn't generate an error inside template code otherwise.

You should see both the msg and BOOST_STATIC_ASSERT_FAILURE in the error
message output in most cases, but as ever it depends a lot on the compiler.

One known defect: 

Borland refuses to inline functions containing BOOST_STATIC_ASSERT_MSG, I
guess this is easily fixed with a

#if defined(__BORLANDC__) && defined(_NDEBUG)

section.

Thoughts?

Comments?

- John Maddock
http://ourworld.compuserve.com/homepages/john_maddock/