On Fri, 25 Feb 2011 23:31:17 -0500, Robert Jacques <[email protected]>
wrote:
On Fri, 25 Feb 2011 22:35:39 -0500, Steven Schveighoffer
<[email protected]> wrote:
On Fri, 25 Feb 2011 19:01:28 -0500, Tomek Sowiński <[email protected]> wrote:
Robert Jacques napisał:
On Fri, 25 Feb 2011 02:48:01 -0500, Kevin Bealer
<[email protected]> wrote:
> I think immutable could benefit from a Value Range Propagation-like
> uniqueness
'unique' has been proposed and heavily discussed before in the news
group.
There even is std.typecons.Unique. Unfortunately, Walter has stated
that
there are issues/difficulties in adding 'unique' to the language.
What were those difficulties?
YATC (yet another type constructor)
Plus, when this was the topic de jour, there were about 3 other type
constructors that were touted as "needed" in order to make unique work
(like "borrowed" and "lent"). Bartosz had a blog post about it. This
meant you had to accept 3 or 4 new type constructors to get unique.
My impression was that it was more than that. Yes, also adding a
'lent/borrowed/scope/no escape' and a 'owned' type would have greatly
eased and empowered unique, but these were all talked about in the same
breath back then. Walter indicated that there was something specific to
unique which was the problem, probably having to do with transitivity.
Ultimately, 'unique/mobile', 'lent/borrowed/scope/no escape' and 'owned'
were all about doing shared memory concurrency better, while the
flagship concurrency model was message-passing.
Unique has other benefits. You can implicitly cast unique to/from
immutable. You can pass a unique reference via a message without it
having to be immutable.
These would benefit thread-local code, and also message passing.
I really like this idea as a way to have unique without the type
constructor: http://d.puremagic.com/issues/show_bug.cgi?id=5081
Well, that not unique. That's a way to gain one of the major benefits
(the building of immutable types) of unique without it. That said, I
also would like it.
Yes, it is a subset of unique, I should have stated it that way.
-Steve
