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Subject: Re: [boost] [Config] Multiple versions of Boost
From: Sohail Somani (sohail_at_[hidden])
Date: 2008-09-13 13:49:26

Bjørn Roald wrote:
> 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.

I am of the opinion that the best and most portable C++ ABI is C. So I
hope the number of occurrences of Boost types in a C++ binary-only
interface is close to 0!

But yeah, two versions of Boost in one TU is asking for it.

>> 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.

I think your bcp patch is overkill just for compiling with a different
namespace. However, it is the best solution for multiple versions in a
single TU. I don't envy that guy's job though...

Sohail Somani

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