Setting array length without initializing/reallocating.

[Sönke Ludwig]

Am 12.12.2020 um 01:53 schrieb Jonathan Levi:
> Wow, there went several hours of debugging.
> 
> Increasing the length of a slice, by setting its length, will initialize 
> the new elements and reallocate if necessary.
> 
> I did not realize length was "smart", I guess I should have guessed.
> 
> Anyway, to work around this, and probably also be more clear, create a 
> new slice from the same pointer.
> 
> `array = array.ptr[0..newLength];`

One way around this is to call `array.assumeSafeAppend();` before 
setting the new length. In this case it will reuse the already allocated 
block as long as it is large enough and only reallocate if necessary.