Accessing array elements with a pointer-to-array

[Steven Schveighoffer]

On Friday, 26 January 2024 at 11:38:39 UTC, Stephen Tashiro wrote:
> On Thursday, 25 January 2024 at 20:36:49 UTC, Kagamin wrote:
>> On Thursday, 25 January 2024 at 20:11:05 UTC, Stephen Tashiro 
>> wrote:
>>>     void main()
>>>     {
>>>        ulong [3][2] static_array = [ [0,1,2],[3,4,5] ];
>>>        static_array[2][1] = 6;
>>>     }
>>
>> The static array has length 2, so index 2 is out of bounds, 
>> must be 0 or 1.
>
> I understand that the index 2 is out of bounds in an array of 2 
> things.  I'm confused about the notation for multidimensional 
> arrays.  I thought that the notation uint[m][n] is read from 
> right to left, so it denotes n arrays of m things in each 
> array.  So I expected that static_array[k][j] would denotes the 
> kth element of the jth array.

I find the following rule very straightforward to explaining it.

If you have an array, it's of type `T[]`. The `T` represents the 
type of each element. When you access element with index `n` of 
this array, it's `arr[n]`, which gives you the `n+1`th `T` 
element in the array.

So how do you match this to a static array `ulong[3][2]`? Well, 
the `T` in this case is `ulong[3]`, and the array part is `[2]`. 
So this is an array of 2 `ulong[3]`.

Therefore, when you index such an array, `static_array[2]` will 
get the 3rd element of this 2-element array, and fail.

-Steve