remove from array

[torhu]

Thorsten wrote:
>> <totaly untested code>
>> 
>> T[] Remove(T)(T[] arr, int i)
>> {
>>    return i==arr.length-1 ? arr[0..$-1] : arr[0..i] ~ arr[i+1 .. $];
>> }
> 
> Sorry, I tried that, and it is too expensive !!
> Because it creates about 3 temporary instances.
> I would say :
> 
> void Remove(T)(inout T[] arr, int i)
> {
>   for(uint j = i;j < arr.length-1;++j)
>     arr[j] = arr[j+1];
>   arr.length = arr.length - 1;
> }
> 
> can someone accelerate this ???

I see Bill already told you about cashew, but here's an answer anyway.

You can use memmove to do the copying.  Using memmove also seems to be 
the fastest way to insert elements in the middle of an array, if you 
need that too.

void Remove(T)(inout T[] arr, int i)
{
   assert(arr && i < arr.length);
   memmove(arr.ptr + i, arr.ptr + i + 1, (arr.length - i - 1) * T.sizeof);
   arr.length = arr.length - 1;
}

If you don't care about the order, you can of course just do this:

arr[i] = arr[$-1];
arr.length = arr.length - 1;