Understanding range.dropBackOne

[Adam Ruppe]

On Tuesday, 28 September 2021 at 22:56:17 UTC, Tim wrote:
> I'm doing the following:
>
> int[25] window = 0;

Note that this array has a fixed size.

> window = someInteger ~ window[].dropBackOne;

Here the window[] takes a variable-length slice of it. Turning it 
from int[25] into plain int[]. Then you can drop one since it is 
variable length. Then appending again ok cuz it is variable. Then 
the window assign just copies it out of the newly allocated 
variable back into the static length array.

> window = someInteger ~ window.dropBackOne;

But over here you are trying to use the static array directly 
which again has fixed length, so it is impossible to cut an item 
off it or add another to it.

> What does the `[]` do exactly? Is an array not a bidirectional 
> range?

It takes a slice of the static array - fetching the pointer and 
length into runtime variables.