2017-09-11 9:50 GMT+02:00 Eike Ziller <[email protected]>: > >> On Sep 11, 2017, at 09:24, Elvis Stansvik <[email protected]> wrote: >> >> 2017-09-10 11:31 GMT+02:00 Elvis Stansvik <[email protected]>: >>> 2017-09-10 11:03 GMT+02:00 Elvis Stansvik <[email protected]>: >>>> Hi all, >>>> >>>> In a quest to find inspiration for good Qt application architectures, >>>> I've been looking at the plugin based one you're using in Qt Creator. >>>> It strikes me as a really nice design. >>>> >>>> I've been reading the available docs on it, and dug into the code a >>>> bit. This may be a bit much to ask, but I was wondering if any of you >>>> devs could answer a few questions that popped up? It would be much >>>> appreciated! >>>> >>>> It's really just two questions, about two different topics: >>>> >>>> 1. The Invoker / invoke<...> Thingie: >>>> >>>> You have ExtensionSystem::Invoker and the associated invoke<..> >>>> helper, which are syntactic sugar for achieving "soft" extension >>>> points. It seems it's not used that much (?). I grepped for >>>> "Invoker|invoke<" in the code and could only find a few uses of it. I >>>> also grepped for "invokeMethod" to see if the approach was being used >>>> "manually" so to speak (without the sugar), and found a few more hits. >>>> >>>> What was the motivation for adding this? I assume it's for cases where >>>> you want a looser coupling between plugins (no linking, no shared >>>> header), but can you give an example of when you really wanted that >>>> looser coupling and why? >>>> >>>> 2. The Plugin System in General: >>>> >>>> Is there anything about the plugin system in its current form, or how >>>> it is used, that you would do fundamentally different if you could do >>>> it all over again? Any areas that you find messy/awkward, that need a >>>> re-think/makeover? In short: What are the biggest warts in the code in >>>> your opinion? >>> >>> As soon as I hit send, I realized I have a third question: >>> >>> 3. Communication Between Plugins: >>> >>> There seems to be two main mechanisms through which plugins >>> communicate: Either objects that implement shared interfaces are added >>> to the plugin manager object pool and picked up by downstream or >>> upstream plugins (in the top-down or bottom-up phase of plugin >>> initialization, respectively), or a singleton instance is acquired and >>> calls made on it. >>> >>> Is the former approach used when dependants provide functionality to >>> their dependees (which are unknown), and the latter approach used when >>> dependees use their dependants (which are known)? Is that the deciding >>> factor? >> >> And finally, a couple of more down-to-earth questions: >> >> 1. ICore, the class is concrete, so why the I in the name? Was it >> abstract at one point? > > Yes historically. > >> How do you decide whether a class should get >> the interface 'I' in its name? > > It’s a mess ;) > I suppose the trend goes to not prepend the ‘I’.
Ok, I figured there was a history :) > >> The same with e.g. IContext, though >> that one at least has a few virtuals and is used as a base class (but >> no pure ones AFAICS, so still concrete). > > Historically these classes where “pure” virtual (except for the QObject base). > We moved to a more “configurable” approach then to avoid the need to create > subclasses for every little thing, while keeping the option open in many > cases. Alright, this is what I suspected. Thanks for confirming. > >> 2. The relatively liberal use of singleton classes. We all know that >> is a debated subject, and I don't have an opinion either way. I'm just >> interested in if you have some (spoken or unspoken) policy regarding >> singletons in the project. Do you want to minimize the use of them, or >> is it OK for newer code, or is it judged on a case-by-case basis? Have >> you had any moments where you really wish you hadn't used singletons? >> (e.g. I know it can sometimes hurt testability). > > We always had a liberal amount of singletons in Qt Creator, and we even moved > most of them to be classes with mostly static methods a while ago. There are > no plans to move away from that. If you have a central hub for “managing” > something, feel free to use a singleton/static methods. Okay. I also personally think the convenience of singletons outweighs their drawbacks in many cases. Nice to see this liberating attitude. Thanks for sharing Eike. Elvis > > Br, Eike > > -- > Eike Ziller > Principal Software Engineer > > The Qt Company GmbH > Rudower Chaussee 13 > D-12489 Berlin > [email protected] > http://qt.io > Geschäftsführer: Mika Pälsi, > Juha Varelius, Mika Harjuaho > Sitz der Gesellschaft: Berlin, Registergericht: Amtsgericht Charlottenburg, > HRB 144331 B > _______________________________________________ Qt-creator mailing list [email protected] http://lists.qt-project.org/mailman/listinfo/qt-creator
