On Tue, Jun 9, 2009 at 11:50 AM, <dherring@ll.mit.edu> wrote:
On Tue, 9 Jun 2009, Zachary Turner wrote:
Here are the build timings on my machine (Visual Studio 2008 Service Pack
2)
RedundantGuard - 1 second compile + link time PragmaOnce - 1 second compile + link time Nothing - 15 seconds compile + link time
...
So, I believe that boost compile times can benefit significantly from this.
Thoughts?
Could you run benchmarks on gcc? Will my compile times suffer for your improvement?
- Daniel
It seems someone else in the thread has already run benchmarks on GCC, but regardless of how the benchmarks did or did not turn out, I can say with 100% certainty that nobody will suffer. That's the exact reason I mentioned that compilers should be whitelisted based on which ones benefit from #pragma once, and only use #pragma once for said compilers. #if defined(_MSC_VER) && (_MSC_VER >= 1020) #pragma once #endif That's all it takes. Everybody benefits. Of course I don't have licenses for every C++ compiler around, but I'm sure there are other compilres in which it benefits also. So I would need some assistance from other people who do have other compilers to help find out which compilers it does offer an improvement on. And of course, the default would be to NOT use pragma once, erring on the side of caution. If you see any downsides to this approach let me know, but it seems like a win/win for everyone. To make it even more explicit, there could even be a global macro, which defaults to undefined, called BOOST_USE_PRAGMA_ONCE. The programmer would be forced to explicitly declare this macro before including any boost headers, and if it is enabled, boost would use pragma once.