Re: Checking if a structs .init value is zero bits only

[Ali Çehreli via Digitalmars-d-learn]

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