I appreciate your comments.
The introduction of a range type (as they appear in slices and foreach)
should not have to introduce new features. A simple int..int (or
uint/long/ulong) 'tuple' would do the trick. Internally the compiler
already has SliceExp with 'lwr' and 'upr' bounds. Exposing this to the
programmer might be useful.
Anyway, probably not useful enough :)
L.
On 29-4-2010 1:04, bearophile wrote:
> Lionello Lunesu:
>
>> Wouldn't it be nice to introduce a built-in for these int..int ranges?<
>
> It was discussed in the past, but there are some design problems.
>
> In theory it can be used to define overload of slices operator as:
> opSliceAssign(int v, Slice s)
>
> A problem is that slices can have more than just size_t indices, this code
> works and 'i' is of type long:
>
> import std.stdio: writeln;
> void main() {
> foreach (i; (long.max - 10) .. (long.max - 1))
> writeln(typeid(typeof(i)), " ", i);
> }
>
> So the (immutable) Slice struct has to be a template:
> opSliceAssign(int v, Slice!size_t s)
>
>
> struct Slice(TIndex) {
> immutable TIndex start, stop;
> immutable int stride; // simplified
> immutable SliceType type;
> this(...) {...}
> // few methods: in operator, length, subslicing, etc.
> }
>
> So it's usually 4 CPU words long on 32 bit CPUs (it can be just 3 words long
> on 64 bit CPUs if stride and type are presented in 32 bit each).
>
> The stride is the third optional value, usually it's 1, its syntax can be:
> start .. stop : stride
>
> The stride is an int because it can be negative. If start and stop are long,
> you can't have a stride larger than an int min-max values.
>
> 'type' is a bitfield that encodes the kind of Slice. I think the cases are:
>
> 1 .. 7
> 0 .. $
> 0 .. $-10
> 1 .. 7 : 2
> 0 .. $ : 2
> 0 .. $-10 : 2
> .. 7
> .. $
> .. $-10
> .. 7 : 2
> .. $ : 2
> .. $-10 : 2
>
>
> (The cases with no start are meant to be useful for intervals infinite on the
> left. I am not sure this is an important group of cases.)
>
>
> The Chapel language generalizes this idea into the idea of "domain", a
> first-class index set.
> I have explained it here, and I think it's an useful idea:
> http://www.digitalmars.com/webnews/newsgroups.php?art_group=digitalmars.D&article_id=87311
>
> Bye,
> bearophile
