`clear`ing a dynamic array
John Colvin via Digitalmars-d-learn
digitalmars-d-learn at puremagic.com
Sat Oct 24 07:18:02 PDT 2015
On Saturday, 24 October 2015 at 13:18:26 UTC, Shriramana Sharma
wrote:
> Hello. I had first expected that dynamic arrays (slices) would
> provide a `.clear()` method but they don't seem to. Obviously I
> can always effectively clear an array by assigning an empty
> array to it, but this has unwanted consequences that `[]`
> actually seems to allocate a new dynamic array and any other
> identifiers initially pointing to the same array will still
> show the old contents and thus it would no longer test true for
> `is` with this array. See the following code:
>
> import std.stdio;
> void main()
> {
> int a[] = [1,2,3,4,5];
> int b[] = a;
> writeln(a);
> writeln(b);
> //a.clear();
> a = [];
> writeln(a);
> writeln(b);
> }
>
> which outputs:
>
> [1, 2, 3, 4, 5]
> [1, 2, 3, 4, 5]
> []
> [1, 2, 3, 4, 5]
>
> How to make it so that after clearing `a`, `b` will also point
> to the same empty array? IOW the desired output is:
>
> [1, 2, 3, 4, 5]
> [1, 2, 3, 4, 5]
> []
> []
>
> ... and any further items added to `a` should also reflect in
> `b`.
D's arrays are not pure reference types, they work like `struct
Array(T) { size_t length; T* ptr; }` with some extra methods and
operators. If you think of them like that it should be clear what
is/isn't possible.
If you want to have two references to the same array, including
the length, use T[]* or a ref argument to a function or wrap it
in a class.
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