• Per =?UTF-8?B?Tm9yZGzDtnc=?= (4/4) Mar 27 2018 Is there a way to check if a struct `S` can be initialized using
• =?UTF-8?Q?Ali_=c3=87ehreli?= (29/32) Mar 27 2018 The following idea should work. One question that I'm not certain about
• Per =?UTF-8?B?Tm9yZGzDtnc=?= (3/22) Mar 28 2018 Yes, of course, thanks.
• Seb (4/8) Mar 27 2018 Have a look at:
• Per =?UTF-8?B?Tm9yZGzDtnc=?= (4/7) Mar 28 2018 Exactly what I wanted. Thanks!

Per =?UTF-8?B?Tm9yZGzDtnc=?= <per.nordlow gmail.com> writes:

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?

=?UTF-8?Q?Ali_=c3=87ehreli?= <acehreli yahoo.com> writes:

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

Per =?UTF-8?B?Tm9yZGzDtnc=?= <per.nordlow gmail.com> writes:

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.

Seb <seb wilzba.ch> writes:

On Wednesday, 28 March 2018 at 00:15:34 UTC, 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?

Have a look at:

https://github.com/dlang/phobos/pull/6024

(review/feedbackon this PR is welcome!)

Per =?UTF-8?B?Tm9yZGzDtnc=?= <per.nordlow gmail.com> writes:

On Wednesday, 28 March 2018 at 01:39:40 UTC, Seb wrote:
 Have a look at:

 https://github.com/dlang/phobos/pull/6024

 (review/feedbackon this PR is welcome!)

Exactly what I wanted. Thanks!

In use here

https://github.com/nordlow/phobos-next/blob/41b9e0dcfbb4eed6b2ee52d0465425556f14c00f/src/open_hashmap_or_hashset.d#L242