On Thursday, 17 October 2013 at 18:00:20 UTC, Vitali wrote:
I expected slices to be in D (http://dlang.org/arrays.html)
like they are in Go
(http://blog.golang.org/go-slices-usage-and-internals). But
they are not.
Why the array have to be reallocated after the length of a
slice is changed? It makes slices useless.
Here a little example (it fails):
void testSlices() {
int[] dArr = [10, 11, 12];
int[] dSlice = dArr[0..2];
dSlice.length++;
assert(dArr[2]==dSlice[2]); // failure
}
As David Eagen said, your problem is that in D, dArr[0..2] is not
inclusive, it's exclusive, so you get dArr[0] and dArr[1].
Changing it to dSlice = dArr[0..3] will work (or better,
dArr[0..$]). However, there's something else going on here that's
fishy:
void testSlices()
{
int[] dArr = [10, 11, 12];
int[] dSlice = dArr[0..2];
writeln(dArr.ptr, " ", dArr.capacity, " ", dArr.length);
writeln(dSlice.ptr, " ", dSlice.capacity, " ", dSlice.length);
dSlice.length++;
writeln(dSlice.ptr, " ", dSlice.capacity, " ", dSlice.length);
writeln(dArr);
writeln(dSlice);
}
4002DFF0 3 3
4002DFF0 0 2
4002DFE0 3 3
[10, 11, 12]
[10, 11, 0]
dSlice says that it has length 2, but accessing dSlice[2] does
not produce a RangeError... Likewise, printing it out prints 3
elements, not 2. This looks like a bug to me.
