[dmd-beta] Hopefully the last betas

[Andrei Alexandrescu]

On 09/16/2010 06:01 PM, David Simcha wrote:
> Basically works for me.  There is one issue, though, that I don't think
> is a showstopper for this release but highlights a very bad long-term
> issue that I'd really like to address sooner rather than later.
>
> In Phobos right now, you can no longer do lowerBound, canFindSorted,
> etc. on a const/immutable array due to 3 bugs in SortedRange. Two of
> these are trivially fixable (look at the code for save() and opSlice())
> but the third isn't. release() calls move() on the range. This doesn't
> work for const/immutable arrays.

This is also easy to fix by guarding release() with a static if.

> In general bug reports are piling up in Bugzilla about how defective
> std.range and std.algorithm are when dealing w/ const/immutable ranges
> and elements. D's lack of tail const makes this essentially impossible
> to deal with on a generic level (though for arrays specifically the fix
> is trivial, but I don't want to just special-case things in supposedly
> generic code). This is an entire class of bugs that we just don't know
> how to fix. Ideas?

I think we should focus, at least initially, on non-constant ranges of 
constant elements. Algorithms expect to mutate their ranges, it's mostly 
how the whole thing works. So we care about ranges of const elements, 
and I don't think we're helpless with those because many ranges are 
templated on their element type a la SomeRange!(const X).

One step forward for const arrays is to do make typeof(arr[]) const(T)[] 
when typeof(arr) is const(T[]). Same with immutable. That way, people 
who have const and immutable arrays only need to append "[]" to their 
array when passing it to some std.algorithm function.

Walter, what do you think?


Andrei