[boost] Re: Library versioning

From: Dave Abrahams (abrahams_at_[hidden])
Date: 1999-12-20 22:23:45

Herb wrote:
> Issue the first: Would this require duplicating object code for unchanged
> components (i.e., double object sizes)? No; simply have a shared
> implementation (which might not even be templated) and write forwarding
> functions. This is usually a good idea when implementing templates anyway, for
> example for the container<void*> technique.

Easier answer: provide using-declarations to import names from older
namespaces into newer ones.

> Issue the second: Say vector<int> didn't change in any way. One problem,
> pointed out to me by Andy Koenig, is that std::vector<int> is not the same
> type as std200x::vector<int> and the code in #2(b) will not work when passed a
> std200x::vector<int>.

It's the same type if you've used a using-declaration.

> Apart from #2(b), I admit I find idea B seductive. Absent a magical new
> feature like namespace inheritance, it is not clear to me how to do achieve
> goal #2(b), but maybe that goal isn't important in itself. Does the solution
> get any better if we use a "white lie" and inherit std200x::vector<T> from
> std::vector<T>, in order to make #2(b) compile when passed a
> std200x::vector<int>? I haven't thought about this at all, but it seems it
> should blow up somehow. You'd probably have to duplicate some or all of the
> free operators, anyway.

Also, there's no way to go in the reverse direction if you do that, as there
should be since the types are really supposed to be equivalent.

-Dave