"Bag" is just a Smalltalk term for an unordered collection. Essentially a context is just a map, with extra logic for tracking dynamic changes, injection, and a notion of a parent context. If the most local context can't supply a value, it delegates to the parent. As Kevin suggested this allows modeling of things like the widget hierarchy where a tab in a view might be one context, the view itself another context, another context for the window, etc, up to a global application context. You're right that the injection logic can (and probably should) be separated from the context logic since it's unlikely to change.
Ed Merks <[email protected]> Sent by: [email protected] 01/07/2009 04:41 PM Please respond to E4 Project developer mailing list <[email protected]> To E4 Project developer mailing list <[email protected]> cc Subject Re: [e4-dev] A missing framework piece: contexts? Oleg, Comments below. Oleg Besedin wrote: “Progress is made by lazy men looking for easier ways to do things”. I'm exceedingly lazy... I think this is exactly how the concept of contexts came to life. Our code runs in some environment; way too often we need to pass tens of arguments from method to method and from class to class just to keep them aware of the environment. To make it easier we are considering adding a concept of "context". At the conceptual level a "context" is a combination of: - a bag that could be stuffed with elements that compose environment, and Couldn't we just use Map<String, Object>? What's the significance of the term "bag"? - a mechanism to inject elements from the bag into your POJO objects Such a mechanism could be independent of how the "bag" itself is implemented. The contexts are organized in a hierarchy. Child context can add service objects that make sense at their level: IEquinoxContext myContext = ApplicationContext.newChild(); Will we expect people to create context with specialized behavior? Which parts will be specialized and why? myContext.addObject("log", myLog); The service objects from the context can be injected into POJO objects using field and method injection: myContext.injectInto(object) resulting in the field object.equinoxLog being set to "myLog". I could imagine a static Injector.inject(Map<String, Object> values, Object target) utility doing all this type of work with no additional interfaces or implementations of those interfaces. Of course then there's be only one implementation of this, which conceptually seems less flexible, but that's the question earlier. What parts of which mechanisms would clients be trying to specialize? Contexts support dynamic events and multiple service objects per ID. What are those? :-P In addition, contexts can be tied into creation of objects from the extension registry and help access OSGi services. I think I'm missing a lot of the picture even looking in the bugzilla. It sounds interesting though... I'd like to raise this subject at the E4 call to see what people think about it. The details of this work can be found in the enhancement request 259423: https://bugs.eclipse.org/bugs/show_bug.cgi?id=259423 Sincerely, Oleg Besedin _______________________________________________ e4-dev mailing list [email protected] https://dev.eclipse.org/mailman/listinfo/e4-dev _______________________________________________ e4-dev mailing list [email protected] https://dev.eclipse.org/mailman/listinfo/e4-dev
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