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Subject: Re: [boost] [system] Header-only Boost.System by default ?
From: Groke, Paul (paul.groke_at_[hidden])
Date: 2017-10-12 08:51:19

> -----Original Message-----
> From: Boost [mailto:boost-bounces_at_[hidden]] On Behalf Of Damien
> Buhl via Boost
> Sent: Dienstag, 10. Oktober 2017 21:54
> Am 10.10.2017 um 10:21 schrieb Groke, Paul via Boost:
> >> [...]
> > And even if the "same address" thing was solvable (which I think it
> > is, although not pretty and it would require interface changes), there
> > is the problem with unloading DLLs/SOs. You'd have to pin every module
> > that contains error categories. Which IMO is a side effect that you
> > really don't expect and want, especially from a header-only library.
> >
> I must be missing something about internal linkage. This problem should
> already exists with the current implementation no ? If you have an
> error_category singleton instance in a TU, then unloading a dll containing this
> TU should also lead to having the error_category refer to some incorrect
> memory location then.

You're right. It should work though if it's guaranteed that the module that created an error_code object is still loaded while there's a chance that the object may be accessed. If you add some magic that manages to find an already existing equivalent error_category instance, to solve the "more than one instance" problem, an error_code created in module A might end up referencing the error_category object in module B. Then unloading module B would break error_code objects created by A, which really isn't good.

> Do you know of any example code doing this ?

Doing what exactly?

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