Re: [xwiki-devs] Choosing the default component implementation [take 2]

My opinion on this is that we don't really need it and it's just a new feature on top of what we have (i.e. more complexity and higher risk of not being able to use a standard component framework when one emerges - for example CDI).

Also I'm not fond of the ability to create aliases at execution time (ie in the ComponentManager implementation). It's better to have it at the level of the binding but not as a feature of the ComponentManager. Doing this would ruin any ability to use another component framework in the future. All in all I'm -1 till you prove that this can work at least in the following component models (i.e. that those models have this notion or that it can be added): * Guice (will work if you don't put in the ComponentManager impl since Guice has static manual binding)

* CDI (I don't know how it could work with it) - CDI is our best bet ATM as our future component framework

* OSGi

Thanks -Vincent On Jun 5, 2012, at 7:31 PM, Jerome Velociter wrote: > Hi devs. > > I gave this subject some thoughts and I agree with Sergiu on the general > issue of using "default" hint as a marker for default implementations. > > Jerome > > On Mon, May 21, 2012 at 10:32 PM, Sergiu Dumitriu<sergiu(a)xwiki.com> wrote: > >> Hi devs, >> >> Hmm, time flies, I realized that it's been a month and a half since I >> started this thread, but didn't get to counter-argument so far. Because I >> wanted to give more compelling reasons after I wrote the initial draft of >> the original proposal, I got slammed with counter arguments centering >> mostly on why our current implementation already allows to work around the >> technical difficulties that I presented, although those technical >> difficulties were just extra arguments that weren't actually that important. >> >> Let's start from scratch. >> >> I believe that using "default" as a component hint is in most cases wrong, >> since it doesn't actually say anything about the particular implementation. >> Let's take some examples: >> >> >> EntityReferenceSerializer, with its many implementations: >> - "compact", which creates compact representations that don't repeat the >> parts that are the same as the current document >> - "compactwiki" that only skips the wiki part when not needed >> - "path" which creates references usable as a path on the filesystem or in >> URLs >> - "uid" which creates non-ambiguous representations >> - and "default", which does a... default representation... whatever that >> means... >> So, while the meaning of the other hints can be guessed from their name, >> that's not true for "default". >> >> >> WikiModel, with its only implementation, XWikiWikiModel, labeled as >> "default". First, this "default" is defined in xwiki-platform instead of >> xwiki-rendering, like the components that actually use that component, >> which means that we're defining a component interface without any >> implementation in our "standalone rendering engine", and thus we're using >> "exceptions as normal decision code" which is wrong. Second, this "default" >> actually means "xwiki default". Why can't the hint be "xwiki" instead of >> "default", since that what that implementation is actually doing: "this is >> the model used in XWiki", and not "this is the default model that most wiki >> engines use". When looking up an instance of the WikiModel component, we >> don't request "the default wiki model", but "the wiki model currently in >> use, whichever that is". >> >> >> ConfigurationSource and its implementations: >> - "space" which looks into space preferences >> - "wiki" which looks into wiki preferences >> - "user" which looks at user preferences >> - "xwikiproperties" which looks in xwiki.properties >> - "all" which looks into all the above >> - "void" which is always empty >> - "memory" which stores settings explicitly set by code >> - and "default" which does... stuff... let me get back at you after I look >> into its code to check what it actually does. >> >> >> XHTMLLinkTypeRenderer is an example where "default" does make sense, since >> we have special treatment for "doc"ument, "attach"ment, "mailto", "unc", >> "interwiki", and then there's a "default" that handles all the others, like >> "url" and "path". >> >> >> I was writing a component called UploadedFileManager, which is supposed to >> parse uploaded files from a request, and the implementation for it was >> called CommonsFileUploadManager, since it used the Apache >> commons-fileupload library for the actual request parsing. I don't think >> that calling it "default" is appropriate, since in the 3.0 servlet >> specification the upload behavior is embedded in the specification, in the >> ServletRequest interface, and that seems more "default" than using a >> particular library to do the job. A more appropriate hint is "commons", >> since that's what it actually does: "this implementation handles file >> uploads by using the apache commons library that does that", and not "this >> implementation handles file upload in the default way, which everyone >> should know what it actually is". >> >> >> So, I strongly feel that what the component manager returns when looking >> up a component without a hint shouldn't be the implementation labeled >> "default", but one of the existing implementations, as configured somehow. >> >> >> I'm not yet sure how that configuration takes place, that would be the >> subject of another discussion, but I'd like to get a consensus on whether >> we need this change or not.