Andrei Alexandrescu wrote:
We're entering the finale of D2 and I want to keep a short list of
things that must be done and integrated in the release. It is clearly
understood by all of us that there are many things that could and
probably should be done.
1. Currently Walter and Don are diligently fixing the problems marked on
the current manuscript.
2. User-defined operators must be revamped.
Should opIndex and opSlice be merged?
This would be simpler, and would allow multi-dimensional slicing.
Probably the simplest way to do this would be to use fixed length arrays
of length 2 for slices.
So, for example, if the indices are integers, then
opIndex(int x) { } is the 1-D index, and
opIndex(int[2] x) {} is a slice from x[0] to x[1],
which exactly corresponding to the current opSlice(x[0]..x[1]).
Since fixed-length arrays are now passed by value (yay!) this would be
just as efficient as the current method. It'd be simple to implement.
Downsides: (1) Arguably not terribly intuitive.
(2) This would not let you have a slicing from A..A, while
simultaneously allowing indexing by A[2]. But I don't think that makes
sense anyway -- what would $ return? (Note that it doesn't stop you from
having indexes of type A[2], and slice from A[2]..A[2], which might be
important for containers of 2D vectors. It's only the case where
indexing and slicing are different types, which is prohibited).
This is the only solution I have which doesn't introducing more coupling
between the language and standard library.
Another possible solution is to define a special Slice struct in
std.object; downside is that it creates yet another pseudo-keyword.
A third solution would be to use tuples; currently I think it's
impossible, but if tuple auto-flattening is removed there may be a
chance. Even so, it might be a little clumsy to use.
A fourth solution is to retain the status quo, and not provide the
multi-dimensional slicing feature <g>. This is actually about the same
amount of work as option (1), since opDollar would need to work for
opSlice (I only implemented it for opIndex).
