Re: [picocontainer-dev] comments on injection

Erik

I've thought about this since you penned it.

Inversion of Control suggests that control is good ( in a certain  
direction).  getComponent(..) returning instances for formerly  
unregistered components is bad for mutiple reasons:

   1) you've lost the explicit registration step, meaning the audit  
of what's being used is not clear
   2) there recursive nature of deps ( Apple needs Banana needs  
Orange ) can not adequately tell which constructor to use.  Should it  
aim at the simplest (no args) or the greediest as a strategy?
   3) mixing of DI types.  if a Annotation DI Apple needs Banana or  
Orange, should they be the same injection type? or same with a  
fallback of CDI ?

Finally,

The whole thing is doable without ComponentLocator changes  :

public class MagicLocatingPicoContainer extends DefaultPicoContainer {
   // ctors ..
   public Object getComponent(Object key) {
      Object inst = super.getComponent(key);
      if (inst == null) {
          addComponent(key);
          return super.getComponent(key)
      } else {
         return inst;
      }
   }
}

Thoughts?

- Paul


On Jun 1, 2007, at 1:46 PM, Putrycz, Erik wrote:

> Here is another expanded testcase and more doc.
>
>
> Erik.
>
> From: Paul Hammant [mailto:[email protected]]
> Sent: June 1, 2007 16:20
> To: dev-qxt/[email protected]
> Subject: Re: [picocontainer-dev] comments on injection
>
>
> Expand that a little more with testcode will ya Erik?
>
>
> -ph
>
>
> On Jun 1, 2007, at 11:21 AM, Putrycz, Erik wrote:
>
>
>
>
> My other (main) use case is injection…
>
> When I have
>
> @Inject
>
> private MyClass _myClass;
>
>
> If MyClass is not registered then it gets registered automatically  
> in Pico. With this feature, I hardly have any “initialization” code  
> in my projects. I just start my project by creating a container and  
> everything else gets wired automatically. I’m not sure how this  
> could work out with “getInstance”.
>
>
> Erik.
>
> From: Paul Hammant [mailto:[email protected]]
> Sent: June 1, 2007 13:27
> To: dev-qxt/[email protected]
> Subject: Re: [picocontainer-dev] comments on injection
>
>
> What other usecase is there Erik ?
>
>
> For the one you;ve given :-
>
>
> +          @Test
>
> +          public void testDynamicRegistration() {
>
> +                      MutablePicoContainer pico = new  
> DefaultPicoContainer();
>
> +                      ComponentLocator dynamicReg = new  
> DynamicRegistrationLocator();
>
> +                      pico.addLocator(dynamicReg);
>
> +                      LinkedList<String> list = pico.getComponent 
> (LinkedList.class);
>
> +                      assertNotNull(list);
>
> +          }
>
>
>
> I might prefer ..
>
>
> +          @Test
>
> +          public void testDynamicRegistration() {
>
> +                      MutablePicoContainer pico = new  
> DefaultPicoContainer();
>
> +                      LinkedList<String> list = pico.addComponent 
> (LinkedList.class).getInstance();  // getInstance() is new and  
> implicitly on the last component added ~  v easy to implement
>
> +                      assertNotNull(list);
>
> +          }
>
>
> I know you have a 'bigger' use of your way up your sleeve :-)
>
>
> - Paul
>
>
> On Jun 1, 2007, at 9:46 AM, Putrycz, Erik wrote:
>
>
> <Pico2-locator.patch>
>
>
>
>
>
>
> <Pico2-locator.patch>
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