On 05.06.2012 9:33, Roman D. Boiko wrote:
On Tuesday, 5 June 2012 at 05:28:48 UTC, Roman D. Boiko wrote:
... without deep analysis I can't come up with a good API / design for
that (without overcomplicating it). Probably keeping mutable and
immutable APIs separate is the best choice. Will return to this
problem once I get a bit of free time.
Simplest and possibly the best approach is to provide an immutable
wrapper over mutable implementation, but that may be difficult to make
efficient given the need to support insert / delete as common operations.
I suspect I would have to add another policy like Persistent that will
preallocate some slack space implicitly so that some pages can be
shallowly copied on each assign(a-la COW) and immutable parts still reused.
Another simpler way would be to use an separate field "pointer-to-actual
base" for each level, thus allowing it to redirect it away to new
(modified) copy. Still looks like policy as it _maybe_ slightly slower.
Anyway as a start this should work:
auto modifyDupGlobalImmutableTrie(Trie(immutable(T), ...) t
, scope delegate(Trie(immutable(T), ...) )pure dg) __pure__
{
auto copy = t.dup;//this would be one day a shallow copy
with(copy)
{
dg(copy);
}
return copy;
}
//later on
{
...
immutable newTrie = modifyDupGlobalImmutableTrie(yourTrie);
...
}
--
Dmitry Olshansky
