Enums and immutables

[ag0aep6g via Digitalmars-d-learn]

On 03/18/2017 01:22 PM, Oleg B wrote:
>     enum arr = cast(ubyte[])[0,0,0,1,0,0,0,2,0,0,0,3,0,0,0,4];
>
>     auto arr1 = cast(void[])arr;
>     immutable arr2 = cast(immutable(void)[])arr;
>     enum arr3 = cast(void[])arr;

Aside: The casts here do nothing to affect the outcome.

>     writeln(cast(ushort[])arr1); // [0, 256, 0, 512, 0, 768, 0, 1024]
>     writeln(cast(ushort[])arr2); // [0, 256, 0, 512, 0, 768, 0, 1024]
>     writeln(cast(ushort[])arr3); // [0, 0, 0, 1, 0, 0, 0, 2, 0, 0, 0, 3,
> 0, 0, 0, 4]

I guess the last one here is supposed to be the surprising one. I find 
them all surprising, actually.

`arr` itself is already not what I'd expect. It should be an array with 
64 elements, because you're casting an array of 16 int elements to 
ubyte[] (16 * int.sizeof = 64).

At least that's how it works with a run-time array:

     auto a = [0,0,0,1,0,0,0,2,0,0,0,3,0,0,0,4];
     auto b = cast(ubyte[]) a;
     assert(b.length == 64);

But when the source is a literal or an enum, the cast doesn't change the 
length. Instead the elements are casted individually. I'd call this a 
bug. It's definitely surprising.

It's also potentially throwing data away:

     writeln(cast(ubyte[]) [257, 2, 3, 4]); /* [1, 2, 3, 4] */

Run-time array casts don't do that.