> At a purely practical level, I'm constantly wishing I could dynamically
> change an ArrayList into a LinkedList without having to know about all the
> places that might hold a reference to it.


A good example of a problem that can be completely eliminated: use a
Finger-Tree-based sequence for all sequences, then there is no need to worry
to convert from one sequence type to another (of course, the items still
need to be of the same type). Not to mention the gains in efficiency.

Here by Finger-Tree I mean the structure defined by Hinze & Patterson in
their paper:

      http://www.soi.city.ac.uk/~ross/papers/FingerTree.pdf

For a recent C# implementation of a Finger-Tree, see my blog. The
performance comparison results of a Finger-Tree-based sequence to .Net
sequences or XPath sequences as implemented by three XSLT 2.0 processors are
also instructive (although having in mind the efficiency of operations with
a finger-tree, these should have been fully expected).



-- 
Cheers,
Dimitre Novatchev
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Truly great madness cannot be achieved without significant intelligence.
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To invent, you need a good imagination and a pile of junk
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Never fight an inanimate object
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You've achieved success in your field when you don't know whether what
you're doing is work or play