Re: [boost] Making two Boost libraries interoperate

On Thu, 25 Apr 2019 at 03:40, Edward Diener via Boost wrote:

On 4/24/2019 2:42 PM, Rene Rivera via Boost wrote:

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On Wed, Apr 24, 2019 at 1:34 PM Robert Ramey via Boost wrote:

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On 4/24/19 10:54 AM, Rene Rivera via Boost wrote:

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On Wed, Apr 24, 2019 at 11:45 AM Robert Ramey via Boost wrote:

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On 4/24/19 8:56 AM, Joaquin M López Muñoz via Boost wrote:

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Not sure if this helps, but the way I did it in Boost.Flyweight is by isolating all serialization code in a separate header:

https://www.boost.org/libs/flyweight/doc/reference/flyweight.html#serialize_...

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This does help! or it would help if our dependency tools understood this. In particular flyweight library is not dependent on the serialization libraries. Only apps which use the flyweight library AND the serialization library are dependent on the serialization library. Our notion of "dependency" obscures this.

It's only "our notion" in the sense that they mirror the notion of dependencies that users of *external* package managers, dependency managers, and users thereof have.

Right. I don't mean to suggest that it's only boosts problem. It's a problem in the assumptions that all these packages make. As more and more projects are built by composition of more and more libraries (a good thing!) It becomes apparent that the original "naive notion" breaks down. That's what we're seeing.

The limit of your suggestion/desire amounts to making all source code globally available as individually addressable TUs. That limit is untenable to almost all developers. And hence the line must be drawn some place in between. The existing PDMs have draw it at the published logical boundaries. For the rather same rationale that it's easy to reason about for the end-users. And it's the end-users we are trying to satisfy. I.e. it's not a "naive notion". It's an experientially derived at end-user oriented method.

In theory you may be right but in practice I side with Robert Ramey. If I know that when using library X I will not be including a particular header file which creates a dependency on library A, which itself has dependencies on library B and C, then my practical view is that using library X does not depend also on libraries A, B, and C, even when some dependency report says that library X depends on libraries A, B, and C. Therefore the dependency report is not applicable in my particular case.

e.g. when using just #include or together with #include then MP11 does not or does depend on MPL. I side with Robert then too. I think this (and the flyweight above) opt-in approach is something worth to consider and strive to refactor libraries accordingly. Best regards, -- Mateusz Loskot, http://mateusz.loskot.net