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From Stephen Colebourne <scolebou...@btopenworld.com>
Subject Re: [collections] suggested extensions to package oacc.iterator
Date Thu, 02 Mar 2006 17:58:03 GMT
> Looking for a way, to turn any existing iterator into one,
> that can be exercised repeatedly, I stumbled upon the classes/if's
> ResettableIterator, AbstractIteratorDecorator, and ListIteratorWrapper,
> but didn't actually found an elegant solution for this. Obviously, the
> simplest option to include something like this into collections, was to
> turn ListIteratorWrapper into a ResettableIterator by implementing the
> reset() method.
I'd welcome an patch for this with tests.


> 1.)
> A derivation of AbstractIteratorDecorator, with the only function to
> record the returned elements,
> as they are traversed - candidate name: CachedIterator or
> CachedIteratorDecorator.
> This Decorator would use a List as cache, which could either be
> injected, or created automatically;
This sounds no different to ListIteratorWrapper, or 
IteratorUtils.toList(). IMHO, [collections] is probably over abstracted now.

> 2.)
> An Iterator, that wraps a list similar the manor, ArrayIterator wraps access
> to an array, with the possible extension, that reset() and add() would
> be supported too.
Why not just call iterator() on the List object? Perhaps you mean a 
ResettableIteratorWrapper, which could be useful.

> 3.) Combining the two into ResettableCachedIterator (involves using
> ChainedIterator to do the trick)
> I'm suggesting to use the infix 'Cached' here, because there is the
> possibility of a completely different implementation of a decorator
> allowing resettability: by passing a factory, that is reproducing the
> underlying iterator on reset, if necessary; The difference is obvious:
> the cached approach is guaranteed to reproduce the sequence of elements
> exactly, the factory appraoch is not;
This is probably best achieved as a patch to ListIteratorWrapper.

> 4.) Retrofitting ListIteratorWrapper, to use 1.) and 2.)
Changing a superclass is a binary incompatible change, so we couldn't do 
that.

> 5.) Writing a Decorator, that converts a ResettableIterator into a
> LoopingIterator
Could be done but probably of limited value.

Stephen

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