Re: [platform-ui-dev] arrays and generics in JFace

[Hendrik Still <hendrik.still@xxxxxxxxx>]

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This is a nice approach, I'll see how I'll use this in my changes. Thanks

Regards,
Hendrik

Am 29.07.2013 14:44, schrieb Nigel Westbury:
> Hi Hendrik,
> 
> I have recently completed the adding of generics to the
> databinding bundles.  The way I approached this problem was to add
> a new method that uses Collections and deprecated the method that
> takes arrays.  We use @SuppressWarning only on deprecated code, so
> unless the users are using deprecated code we can be sure that we
> are not breaking the types.
> 
> There is of course the issue of performance.  In my opinion cleaner
> code generally trumps questionable performance gains, but that
> would be a case-by-case decision.
> 
> It is really good to see generics being added to JFace viewer.
> JFace viewer was a large source of problems when adding generics
> to databinding.  I initially parameterized JFace collections with 
> <Object>.  However that did not make it easy for the consumers who
> would often have collections parameterized by something else, but I
> was able to loosen the parameterization a little by making all the
> immutable collections be parameterized by a super class <? super E>
> to the element type in the underlying collection <E>.
> 
> Another thing I ran against is that there are three methods that
> return values with parameterization that is too loose.  These are
> Class.cast, Class.getComponentType, and Array.newInstance.   If you
> look in the e4 databinding repository at
> org.eclipse.jface.databinding.util.Util, you will see the
> following:
> 
> @SuppressWarnings("unchecked") public static <E> Class<E>
> getComponentType(E[] a) { return (Class<E>)
> a.getClass().getComponentType(); }
> 
> @SuppressWarnings("unchecked") public static <E> E[]
> createArrayInstance(Class<E> componentType, int size) { return
> (E[]) Array.newInstance(componentType, size); }
> 
> So at least the warnings are isolated.
> 
> Let me know if there is anything I can do to help.
> 
> Nigel Westbury
> 
> On 26/07/2013 19:22, Lars Vogel wrote:
>> Based on an offline discussion with John, I think
>> @SuppressWarning is the better approach as this avoid the
>> unnecessary object creation.
>> 
>> Best regards, Lars
>> 
>> Am Freitag, 26. Juli 2013 schrieb Hendrik Still :
>> 
> Hi, I'm currently adding generics support to the JFace Viewer. But
> run into problems with the generic typisation of mostly object
> typed arrays. I know arrays and generics do not mix very well. But
> I'm not able to replace arrays by lists, because this would break
> the compatibility top older versions.
> 
> But how should I type/cast the arrays correctly?
> 
> Here is an example from the 
> org.eclipse.jface.viewers.LabelProviderChangedEvent Classe: 
> ------------------------------------------------------------
> 
> private Object[] elements; //... public
> LabelProviderChangedEvent(IBaseLabelProvider source,
>>> Object
> element) { super(source); this.elements = new Object[1]; 
> this.elements[0] = element; }
> 
> ------------------------------------------------------------
> 
> First solution would be this: 
> ------------------------------------------------------------ 
> private E[] elements; //... public
> LabelProviderChangedEvent(IBaseLabelProvider<E> source, E element)
> { super(source); @SuppressWarnings("unchecked") this.elements =
> (E[]) new Object[1]; //Warning this.elements[0] = element; } 
> ------------------------------------------------------------
> 
> Second would be this: 
> ------------------------------------------------------------ public
> LabelProviderChangedEvent(IBaseLabelProvider<E> source, E element)
> { super(source); ArrayList<E> arrayList = new ArrayList<E>(); 
> arrayList.add(element); this.elements = (E[]) arrayList.toArray(); 
> } ------------------------------------------------------------
> 
> What do you think is the better solution in the case of the JFace 
> Toolkit? Or do you have a better idea to solve this problem?
> 
> Regars, Hendrik
> 
> 
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>> 
>> 
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> 
> 
> 
> 
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