Sohail Somani skrev:
Steven Watanabe wrote:
AMDG
Sohail Somani wrote:
Sohail Somani wrote: [snip]
What if Boost.Config did something like:
#if !defined(BOOST) # define BOOST boost #endif
And we replace all uses of the boost namespace with BOOST?
Would such a patch against trunk be acceptable? What are the problems?
In order to make this work we need to make sure that there is a namespace alias where appropriate:
#if !defined(BOOST_NAMESPACE) #define BOOST_NAMESPACE boost #endif
#define BOOST_NAMESPACE_boost 0
#if BOOST_PP_CAT(BOOST_NAMESPACE_, BOOST_NAMESPACE) namespace BOOST_NAMESPACE {} namespace boost = BOOST_NAMESPACE; #endif
#undef BOOST_NAMESPACE_boost
Indeed, you are right. Clever too :-)
There is one obvious problem I see with the -DBOOST_NAMESPACE=foo approach: there is no way to include two versions of Boost within the same translation unit. Unfortunately, I don't think there would be any acceptable way to do this. Though I'm sure you will come back with a way to do it!
Even if you solve this for the namespace, you can not safely have side-by-side headers from two boost versions in the same translation unit. You still have the issues of include paths and all the other BOOST_ preprocessor symbol definitions. There are probably other issues as well that is off my radar screen. Namespace variations only solve part of the issues, but if you don't mix boost versions in the same translation units you may be Ok. However, if you need to use boost types in interfaces used across boost versions -- then you need a different solution. The types need adapters, or they need to be aliased and binary compatible.
By the way, I've received a message on IRC telling me that Xalan and Xerces do something very similar so it wouldn't be totally unprecedented
I was never pleased with the limitation of the Xerces method. So, some years ago I did some testing with a different approach to solve this. I used a patched version of the bcp tool to manipulate names of preprocessor symbol names, include paths, and namespace names in a copy boost (or of selected boost libriaries) copied with bcp. I did some promising tests and posted a patch to the list. I think Eric Niebler reported some success in using this approach. -- Bjørn Roald