Checking if a structs .init value is zero bits only

[Per Nordlöw]

On Wednesday, 28 March 2018 at 00:50:31 UTC, Ali Çehreli wrote:
> On 03/27/2018 05:15 PM, Per Nordlöw wrote:
>> Is there a way to check if a struct `S` can be initialized 
>> using zero bits only, so that we can allocate and initialize 
>> an array of `S` in one go using `calloc`? If not, what should 
>> such a trait look like?
>
> The following idea should work. One question that I'm not 
> certain about is whether padding bytes inside .init can ever be 
> non-zero in D. I assumed they are always zero. If not, the same 
> idea must be applied recursively to individual members.
>
> bool allZeros(T)() {
>     // Yes, this can be implemented as a range algorithm. :)
>     T t;
>     foreach (b; (cast(ubyte*)&t)[0..T.sizeof]) {
>         if (b) {
>             return false;
>         }
>     }
>     return true;
> }

Yes, of course, thanks.

But my goal is (always) to have it done at compile-time.