On Tue, 2004-04-13 at 18:25, Stephen McConnell wrote:
> Hi Marcus!
>
> I've got some general questions about selection that perhaps you or
> other could fill me in on. First off - I'm separating out in my head
> three different things:
>
> 1. the interface we use for locating something (lets call
> it Locator for the purpose of discussion)
> 2. the interface used to supply and instance of a Locator
> to a component
> 3. the sort of information that a component can include
> in a locate request and the expected behavior of
> container in resolving such a request
>
> Item (3) is the thing that IMO needs to be expanded on. Here is a
> couple of examples of an invocation followed by a couple of questions.
> Please not that I'm also not really worried about the argument or
> signatures just yet - so don't pay any attention to the approach - I'm
> in information gathering stage!
>
> public void someDeliveryMethod( Locator locator )
> {
> Map map = new Hashtable();
> map.put( "color", "red" );
> Football football = locator.locate( Football.class, map );
> }
>
> In the above the component implementation has to assume that a container
> has been configured such that "color" is understood - i.e. is
> translatable to something that will help in the determination of the
> appropriate instance to be returned.
>
> Possible interpretations:
>
> 1. color is an attribute of a component type
> 2. colour is an attribute of a service implemented by a
> a component type
isn't the service already identified uniquely by the interface?
> 3. color is a feature attributed to a component model
> (i.e. component model x has configuration y and is
> tagged with attribute color=red)
yes
I think this also comes closest to what selectors offer, which allow the
same implementation class with different configurations to be assigned
different (excuse the word) hints.
> 4. color is an attribute used by a selection handler
> that knows about the Football class
Maybe, but this requires extra work.
>
> Some questions:
>
> 1. if color is understood by a container, but no solution
> are resolvable - is that a failure or is the container
> obliged to return at least some football
failure
>
> 2. which leads to the question .. should we be describing
> a Query object instead of a map? E.g.
>
> Constraint color = new Constraint( "color" );
> color.setRequired();
> color.setValue( "red" );
> locator.locate( Football.class, new Query[]{ color } );
don't know.
As Carsten pointed out, it might well be that a simple key assigned to a
component model is all we need. Until know, I haven't encountered the
need for more complex queries yet (but also hadn't thought about the
possibility).
--
Bruno Dumon http://outerthought.org/
Outerthought - Open Source, Java & XML Competence Support Center
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