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From Greg Brown <gkbr...@mac.com>
Subject Re: let Sequence<T> extend Iterable<T> ?!?
Date Mon, 19 Apr 2010 13:14:26 GMT
>> This approach allows us to combine collection behaviors without collisions on the
Iterable type (for example, org.apache.pivot.xml.Element implements List<Node> and Dictionary<String,
String>, which wouldn't compile if Dictionary also implemented Iterable).
> 
> I didn't suggest that Dictionary<K,V> should implement Iterable.
> I would not be feasible anyway: should it iterate on the keys or the values?

Map<K, V> iterates over keys (since it extends Collection<K>).

Pivot's collections all follow the same pattern:

List<T> : Sequence<T>, Collection<T>
Map<K, V> : Dictionary<K, V>, Collection<K>
Set<E> : Group<E>, Collection<E>

It wouldn't make sense to make Sequence iterable, since Lists are iterable (via Collection).

> Iterating over a list using indices is sooo 90ies. Why can't I simply write:
> 
> for (Object row : tableView.getSelectedRows()) {
>  ...
> }

That's true, but getSelectedRows() is primarily meant to be a convenience method. The primary
means of obtaining a table view's selection is getSelectedRanges(). This method returns an
instance of ListSelectionSequence, which could (and probably should) implement Iterable. 

You might suggest that getSelectedRows() return a List. We don't do this because it might
imply that the return value is a "live" collection to which the caller can listen for updates,
which is not the case.

> Note that a developer who is unaware of the current implementation of getSelectedRows()
could even write the following:
> 
> for (int i = 0; i < tableView.getSelectedRows().getLength(); i++) {
>    Object row = tableView.getSelectedRows.get(i);
>    ...
> }
> 
> which performs horribly because the selected rows are copied to a new ArrayList in a
for loop in each iteration.

I agree - these methods should be better documented.




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