On 2009-11-22 19:58:37 -0500, Andrei Alexandrescu
<seewebsiteforem...@erdani.org> said:
It's very simple, really. Appending to an array never results in
overwriting elements of an existing array. Appending may terminate a
sharing relationship. This is simple, easy to understand, and requires
no understanding of the optimization paraphernalia, which I hope to be
able to improve.
I think it's the "may terminate" part Bartosz (and some others) don't
like, since it's hard to predict and may cause bugs that appear in an
hard to understand pattern when misused.
I'm not exactly sure where to stand on this issue, but I might have a
solution that looks like a compromise: use the MRU only for arrays of
immutable elements, like strings. Since it's not possible to modify
immutable data, it doesn't change the semantics if two slices are
aliasing each other or not[^1]. Other arrays could get the more
predictable behavior of always reallocating, but an optimizer could
still avoid that when static analysis can prove that only one slice
points to the data.
[^1]: It changes things somewhat if you take the address of elements
and start comparing them, but I find it reasonable that taking address
of things could reveal implementation details. It could change things
if the element type has a postblit function, or a destructor, since you
will avoid some copying, but I think that's fine.
--
Michel Fortin
michel.for...@michelf.com
http://michelf.com/
