Checking if a structs .init value is zero bits only

[Ali Çehreli]

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;
}

unittest {
     static struct A {
         int i;
         long l;
     }
     static struct B {
         double d;
     }
     assert(allZeros!A);
     assert(!allZeros!B);
}

void main() {
}

Ali