I don't like slices in D

[Ali Çehreli]

On 10/17/2013 11:41 AM, Vitali wrote:

 > On Thursday, 17 October 2013 at 18:29:47 UTC, John Colvin wrote:
 >> 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
 >>>  }
 >>
 >> What's the use case for this? I haven't found myself ever needing
 >> something like that so far, but i'd be open to seeing an example.
 >
 > The use case is:
 >
 > void appendElement(ref int[] arr, int x) {
 >    arr ~= x;

That will not allocate if there is capacity.

 > }
 >
 > void removeElement(ref int[] arr, int index) {
 >    arr = arr[0..index] ~ arr[index+1..$];

It must necessarily allocate, right? How does Go deal with that case?

However, I see that the capacity of arr after that operation is just 3! 
Since a new array is allocated by the runtime, the capacity of arr could 
be larger as well.

Perhaps that's the only problem here. (?)

 > }
 >
 > void main() {
 >    int[] arr = [1, 2, 3];
 >    arr.reserve(7);       // Reserve capacity.
 >    arr.appendElement(4); // Here should be
 >    arr.removeElement(1); // no realocation of array,
 >    arr.appendElement(5); // but it is.
 >    assert(arr[1] == 3);
 >    assert(arr[2] == 4);
 >    assert(arr[3] == 5);
 > }
 >
 > But maybe I don't understand what slices are for in D. Anyway in Go this
 > works whithout reallocation.

Ali