On 20/10/2013 09:04 a.m., Larry Evans wrote:
On 10/20/13 06:23, Larry Evans wrote: [snip]
Christopher Schmidt used the preprocessor to implement a variadic fusion using the help of the preprocessor to lessen compile times but, IIUC, he used some method (I'll call it "chunking") so that the preprocessor didn't have arbitrary limits:
http://lists.boost.org/Archives/boost/2012/03/191091.php
NOTE: I tried the link in that post to Christopher's code and it no longer works :( However, I'm sure Christopher (if you can find his email address) would be able to supply an update location for the code. You might could use the chunking method to minimize the compile times.
The code here:
http://svn.boost.org/svn/boost/sandbox/variadic_templates/sandbox/slim/
might be helpful. It was based on Chrisopher's code but had to be modified slightly as mentioned in the post:
http://comments.gmane.org/gmane.comp.compilers.clang.devel/24145
which also mentions the slow compile times when not using the preprocessor.
Compilers appear to have improved since then! I decided to take gcc4.8.1 and fusion::map for a spin, since I happen to have a variadic implementation of map that does not use recursion. The results of this crude exercise can be found here: https://gist.github.com/K-ballo/a44590159133997abcdc What I read from them is that each technique reduces compile-time and memory usage in the order I'd expected (C++98 > C++98 preprocessed > C++11 recursive > C++11 non-recursive), contrary to what this thread seems to be saying. Additionally, instantiating a 255 element variadic non-recursive map and getting to the middle of it takes only slightly more time and just 1.3x the memory it takes doing the same for a 50 element C++03 preprocessed map. There's lots of potential in variadics, as long as they are implemented carefully. Regards, -- Agustín K-ballo Bergé.- http://talesofcpp.fusionfenix.com