Change representation of dynamic arrays?

[Janice Caron]

On 10/20/07, Daniel Keep <daniel.keep.lists at gmail.com> wrote:
> but what
> about slicing code?  I know that I use a lot of [lower..$-something]

While this may be optimised for simple arrays, it poses much more of a
problem for classes and structs which override opIndex() and
opSlice(). The problem is that indeces in those functions are always
specified as being relative to the beginning - there is no way to
specify that an index should be considered relative to the end - so
when you do a[0..$-1] in such a struct, the compiler has to convert
$-1 into (a.length()-1). Then, inside opSlice(), to turn it back to a
pointer you'd have to do (start+index).

I know adds and subtracts are not that expensive, but given that this
change is being talked about /because/ we want to get rid of a
subtract, it is worth thinking about this.

Presumably this will all sort itself out if we get iterators? When
that happens, slice expressions could be rewritten by the compiler as
iterator operations, which in turn would call opDereference() or
opRange(), taking iterator parameters. Is that likely to happen, or
will user-defined types always take the slow route?