I appreciate the power of attributes and I think we should consider supporting them very seriously. But before we do that, we need to figure out the hourse-cart relationship between [clazz] and doclet-based metadata.
Will doclets be *the* design for [clazz] or *a* pluggable implementation? If we choose to commit [clazz] to the doclet approach, 1. We have to have source code processing as a mandated part of the build process. 2. We cannot add or modify metadata for pre-existing or code-generated classes. 3. We still haven't answered the requirements for DynaBeans, Maps where there is no source code to augment with doclets. IMO, we should allow a doclet-based plug-in, but it should be a specialization of a more generic mechanism. - Dmitri ----- Original Message ----- From: "Berin Loritsch" <[EMAIL PROTECTED]> To: "Jakarta Commons Developers List" <[EMAIL PROTECTED]> Sent: Saturday, October 26, 2002 4:33 PM Subject: Re: [clazz] Type-based or instance-based metadata? > Dmitri Plotnikov wrote: > > Berin, > > > > ----- Original Message ----- > > From: "Berin Loritsch" <[EMAIL PROTECTED]> > > To: "Jakarta Commons Developers List" <[EMAIL PROTECTED]> > > Sent: Friday, October 25, 2002 11:57 PM > > Subject: Re: [clazz] Type-based or instance-based metadata? > > > > > > > >>Dmitri Plotnikov wrote: > >> > >>>Another dilemma we'll have to resolve is whether metadata will be > >>>type-based, instance-based or both. > >>> > > <skip/> > > >>Most meta info that is useful is type based, not instance based. > > > > I guess my examples are not very convincing. What I am trying to say is > > that type-based metadata is only as detailed as the type. For example, if > > you declare a property as "int" you have said quite a bit about the > > property, however if you declare it as "Object" you have said almost > > nothing. Better yet, all DynaBeans are of the same type - DynaBean. > > Looking at the type says nothing at all. Same with Map. > > > > > >>What you are looking at is instance based reflection info. Not a more > >>generic meta info. > > > > First, we do want to have more metadata than mere reflection. We would like > > to capture information on how to store XML with Betwixt or JAXB, how to > > access objects with JXPath etc. > > > > Second, we are looking to support a wider variety of object models than can > > be supported via Java reflection alone (DynaBeans, Maps etc) > > Then focus on an "extension" of the Class object (I know it is declared final, > so inheritance is out of the question), that has a set of "attributes". These > attributes mean different things to different people/contexts. Also, don't think > of attributes as a simple name=value pair. C# attributes have the concept of > parameters as well as the attribute itself. For example: > > /** > * @avalon:component > * @avalon:role=org.apache.excalibur.DataSourceComponent > * @avalon:creation-policy=singleton > * @test:multi-value=value1,value2,value3 > */ > > This would declare a class to have the "avalon:component" attribute, the > "avalon:role" attribute with the value set to "org.apache.excalibur.DataSourceComponent", > etc. > > These attributes can be read from the IClass (BTW, I hate prefixed interfaces/etc.-- > interfaces should be your primary type, so if we have any idioms put it on the > implementing class). Attributes that are method specific would be put in the > javadoc for your method. In your case you want to know the type info for a DynaBean > return value: > > /** > * @dynabean:return=java.util.Date > */ > Object getDate(); > > You would want the "dynabean:return" attribute for the "getDate()" IMethod, or whatever > you call it. > > The Attribute approach is very simple, and is easy to use. Its meaning only gives > purpose based on the context. The "test:multi-value" attribute in the first example > would be used in a testing framework so that you can apply the same unit test for a > suite of methods/classes--and they don't even have to set up the same interface (the > Delegate stuff can take care of it). In fact using attributes is a great way to > *generate* JUnit tests automagically! > > > > >>Meta info that is useful to me is things like this: > >> > >>* Creation policy (pooled components, thread local components, singleton > >> components, etc.) > > > > Agreed. > > > > > >>* Required components (i.e. when one component requires a component of > >> another type) > > > > Could you provide more details on this one? > > In Avalon components can require other components to function. An example > would be the DatabaseReader from Cocoon. It reads information from a database, > but uses the org.apache.avalon.excalibur.DataSourceComponent to get the connection > from a pool. By declaring this dependency up front, the attributes for the class > would enable a container to ensure that an implementation of the required component > existed. If it did not, the container can post a failure notice immediately that > makes sense. > > > -- > > "They that give up essential liberty to obtain a little temporary safety > deserve neither liberty nor safety." > - Benjamin Franklin > > > -- > To unsubscribe, e-mail: <mailto:commons-dev-unsubscribe@;jakarta.apache.org> > For additional commands, e-mail: <mailto:commons-dev-help@;jakarta.apache.org> > > > -- To unsubscribe, e-mail: <mailto:commons-dev-unsubscribe@;jakarta.apache.org> For additional commands, e-mail: <mailto:commons-dev-help@;jakarta.apache.org>
