Re: [e4-dev] A missing framework piece: contexts?

[Alex Fitzpatrick <agfitzp@xxxxxxxxxx>]

GetOffMyLawnJoke new asEmail send

-- 
Alex Fitzpatrick
agfitzp@xxxxxxxxxx
Software Developer - Rational UML Modeling

From:	Chris Recoskie/Toronto/IBM@IBMCA
To:	E4 Project developer mailing list <e4-dev@xxxxxxxxxxx>
Date:	2009-01-08 10:13 AM
Subject:	Re: [e4-dev] A missing framework piece: contexts?

---

Actually the bag concept is general to computer science,
and at least used to be covered in computer science courses back in my
day. You can put things in the bag, but when you pull something out of
the bag you don't know what you're going to get out in what order.

Of course bags didn't get a lot of air time, because lists, sets, stacks,
and queues were all sexier.

You wizened old Smalltalk dudes don't get to claim ownership over everything
ya know ;-)

===========================
Chris Recoskie
Team Lead, IBM CDT and RDT
IBM Toronto

John
Arthorne/Ottawa/IBM@IBMCA

John Arthorne/Ottawa/IBM@IBMCA
Sent by: e4-dev-bounces@xxxxxxxxxxx

01/08/2009 09:58 AM

Please respond to
E4 Project developer mailing list <e4-dev@xxxxxxxxxxx>

To	E4 Project developer mailing list <e4-dev@xxxxxxxxxxx>
cc
Subject	Re: [e4-dev] A missing framework piece: contexts?

"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 <ed.merks@xxxxxxxxx>
Sent by: e4-dev-bounces@xxxxxxxxxxx

01/07/2009 04:41 PM

Please respond to
E4 Project developer mailing list <e4-dev@xxxxxxxxxxx>

To	E4 Project developer mailing list <e4-dev@xxxxxxxxxxx>
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
e4-dev@xxxxxxxxxxx
https://dev.eclipse.org/mailman/listinfo/e4-dev
_______________________________________________
e4-dev mailing list
e4-dev@xxxxxxxxxxx
https://dev.eclipse.org/mailman/listinfo/e4-dev
_______________________________________________
e4-dev mailing list
e4-dev@xxxxxxxxxxx
https://dev.eclipse.org/mailman/listinfo/e4-dev
[attachment "pic08464.gif" deleted by Alex Fitzpatrick/Ottawa/IBM]
_______________________________________________
e4-dev mailing list
e4-dev@xxxxxxxxxxx
https://dev.eclipse.org/mailman/listinfo/e4-dev