Containers

[Per Nordlöw]

On Wednesday, 1 September 2021 at 02:08:40 UTC, max haughton 
wrote:
> layout. The most profitable example of that I can think of is 
> automatically switching arrays of POD types to be a struct of 
> arrays internally. This transformation makes random access to 
> elements slower, however (say) loops where access to a subset 
> of the elements dominates then this is much faster due to 
> improved cache efficiency.

Speaking of which, here's my D implementation of struct of arrays 
(SoA):

https://github.com/nordlow/phobos-next/blob/master/src/nxt/soa.d

Peter Kirov has an alternative implementation providing some 
benefits. I've copied it into

https://github.com/nordlow/phobos-next/blob/master/src/nxt/soa_petar_kirov.d

The two implementations should be united.

Note that Petar's SoA-implementation has its `capacity`-property 
functionally deduced  from the `length` property as

```d
/** Returns the current capacity - the current length rounded up 
to a power
     of two. This assumption allows us to save on having a 
separate field.
*/
size_t capacity() const pure @safe
{
     return _length.roundUpToPowerOf2;
}
```

thereby saving a word of (stack) space. That behaviour could be 
opt-in aswell via a template parameter.