Removing elements from dynamic arrays?

[Steven Schveighoffer]

On 4/5/22 11:43 AM, Paul Backus wrote:
> On Tuesday, 5 April 2022 at 14:10:44 UTC, Steven Schveighoffer wrote:
>> I'd implement it probably like this (for D2):
>>
>> ```d
>> auto drop(T)(ref T[] arr, T which)
>> {
>>    import std.algorithm, std.range;
>>    auto f = arr.find(which);
>>    debug if(f.empty) throw ...;
>>    auto result = arr.front;
>>    arr = arr.remove(&f[0] - &arr[0]); // god I hate this
>>    return result;
>> }
>> ```
> 
> I think you can get rid of the ugly pointer arithmetic using `countUntil`:
> 
> ```d
> auto drop(T)(ref T[] arr, T which)
> {
>      import std.algorithm, std.range, std.exception;
> 
>      auto i = arr.countUntil(which);
>      debug enforce(i < arr.length, "Not found");
>      auto result = arr[i];
>      arr = arr.remove(i);
>      return result;
> }
> ```

Yeah, or use enumerate. But it's painful:

```d
auto f = arr.enumerate.find!((v, w) => v[1] == w)(which);
auto result = f.front[1];
arr = arr.remove(result[0]);
return result;
```

I have a lib somewhere which isn't complete that allows remembering 
indexes for elements so you can tease out the original index, but it 
breaks when you use it on strings (of course).

-Steve