[phobos] array.shift for deletion/insertion

[Andrei Alexandrescu]

std.array.insert?

Andrei	

On 2/25/11 5:08 PM, spir wrote:
> Hello,
>
> There is no builtin func to delete or insert one or more elements from
> or into a dynamic array. The reason is probably that providing a
> dedicated idiom may let such an operation look cheap (same reason as for
> refusing 'in' for dyn arrays).
> Still, there is a need for this functionality, to avoid
> * either repetedly coding it when needed, possibly with bugs,
> * or using concat, which copies the whole content instead of the
> necessary part.
>
> For both operations, the actual process is a shift operation on the part
> of the array ranging from a lower bound to the upper end, for an offset
> equal to the deleted/inserted slice's length. We could, I guess, provide
> this shift process builtin. This would allow writing deletion/insertion
> easily, while making it obvious that the operation is costly.
> See example below. What do you think?
>
>
> Denis
>
> void shift (T) (ref T[] array, size_t low, sizediff_t offset) {
> if (offset == 0) return;
> auto len = array.length;
> size_t i;
>
> // move up for insertion: proceed backwards
> if (offset > 0) {
> array.length = len + offset;
> for (i=len-1 ; i>=low ; i--)
> array[i+offset] = array[i];
> }
> // move down for deletion: note offset is negative!
> else {
> for (i=low ; i<array.length ; i++)
> array[i+offset] = array[i];
> array.length = len + offset;
> }
> }
>
> unittest {
> auto a = [0,1,2,3,4,5,6,7,8,9];
> writeln(a);
> // delete [4..6]
> a.shift(7, -3);
> writeln(a); // [0,1,2,3,7,8,9]
> // insert [4..6]
> a.shift(4, +3);
> a[4..7] = [4,5,6];
> writeln(a); // [0,1,2,3,4,5,6,7,8,9]
> }
>