possible memory wasting in array handling

[Olaf Till]

On the help list, a problem came up where a probable memory exhaustion
occured only if some large array operations, with indexing, took place
before (they took place within a called function). This reminded me of
the following possible problem with the current array handling.

The Array class maintains a pointer to (and a length of) a 'slice' of
data in ArrayRep. If a smaller array B is created by continuous
indexing of a larger one A:

A = rand (1, 1000000);

B = A(1:1000);

B references a 'slice' in the data of A, without allocating own memory
for the data. But if A is cleared (or destructed on return from a
function), all of its memory remains allocated, as long as B exists
(even though B needs only a small part of this memory). (Even on
writing into B, Array::make_unique() does not help with this if B is
the only reference to the data.)

Is this behavior considered problematic, or even a bug? It possibly
has caused the said problem on the help list. One possibility would be
to just remove this 'slice' optimization. A more difficult way would
involve to maintain, in ArrayRep, not only a refcount, but also a
notion of the greatest slice referenced by any Array.

Olaf

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