dsimcha wrote:
== Quote from Bartosz Milewski (bartosz-nos...@relisoft.com)'s article
dsimcha Wrote:
The one thing that I think has been missing from this discussion is, what would
be
the alternative if we didn't have this "non-deterministic" reallocation? How
else
could you **efficiently** implement dynamic arrays?
In the long run (D3), I proposed using the "unique" type modifier. If an array
is unique, the compiler knows that there are no slices to worry about, and it
can
use in-place reallocation to its heart content. That pretty much solves the
performance problem.
In the short run (D2), I would suggest sticking to "reallocate on every
extension" semantics (especially in SafeD) and provide a library solution (a la
C++ std::vector) where the performance of appending is an issue.
Probably not a bad idea, since:
1. I've concluded that appending to slices simply can't be made both efficient
and safe.
2. We'll probably get a std.collections anyhow.
3. If you **really** care about performance, you should only append when you
don't know the length in advance. If you know the length, you should always
pre-allocate.
We will have collections and all those good things, but I don't see how
the proposal follows from the feedback. My perception is that this is a
group of people who use D. Bartosz' concern didn't cause quite a riot,
so as far as I can tell there is no big issue at stake. (Add to that the
fact that today's arrays are even _more_ potentially puzzling because,
without the MRU cache, expanding slices may trample over other slices.)
In contrast, slowness of ~= comes time and again to haunt this
newsgroup. Want it or not, people will want to use T[] and ~= to manage
arrays. We could remove the ~= operator and require use of a library
type for appends, but the aforementioned facts suggest that that might
not be the best decision.
One thing that Bartosz didn't mention is that "this unique" is different
than "the other unique", which I think reveals the half-bakedness of the
proposal. "The other unique" that was intensively discussed before is
transitive, meaning that the root reference points to a graph of objects
having no other connection to the outer world. "This unique" is very
different because it's shallow - only the array chunk is unaliased, but
the members of the array don't need to be. This is a very important
distinction.
Andrei
