• wjoe (3/25) Jul 27 2020 I would expect a sizeof 1. Why is its size 16 ?
• Steven Schveighoffer (5/12) Jul 27 2020 Is this inside a function? If so, put `static` on it.
• wjoe (5/18) Jul 28 2020 It was run on the doc page. I suppose the examples are wrapped in
• MoonlightSentinel (3/5) Jul 28 2020 Indeed, see
• wjoe (2/7) Jul 28 2020 Thank you.
• Steven Schveighoffer (8/15) Jul 28 2020 It doesn't necessarily need to be in a unittest block (AFAIK, the
• wjoe (6/21) Jul 28 2020 My reasoning was that a unittest is essentially a function and

wjoe <invalid example.com> writes:

 From the API documentation:

 Create a bitfield pack of eight bits, which fit in one ubyte.
 [...]

 struct A
 {
     mixin(bitfields!(
        bool, "flag1",    1,
        bool, "flag2",    1,
        uint, "",         6));
 }
 
 A a;
 writeln(a.flag1); // 0
 a.flag1 = 1;
 writeln(a.flag1); // 1
 a.flag1 = 0;
 writeln(a.flag1); // 0
 writeln(a.sizeof);


 Application output

 false
 true
 false
 16

I would expect a sizeof 1. Why is its size 16 ?

Source: https://dlang.org/library/std/bitmanip/bitfields.html

Steven Schveighoffer <schveiguy gmail.com> writes:

On 7/27/20 5:49 AM, wjoe wrote:
 struct A
 {
      mixin(bitfields!(
         bool, "flag1",    1,
         bool, "flag2",    1,
         uint, "",         6));
 }

Is this inside a function? If so, put `static` on it.

What you are seeing is the 8-byte frame pointer that comes from inner 
structs so you can access stack variables inside the struct.

-Steve

wjoe <invalid example.com> writes:

On Monday, 27 July 2020 at 12:52:53 UTC, Steven Schveighoffer 
wrote:
 On 7/27/20 5:49 AM, wjoe wrote:
 struct A
 {
      mixin(bitfields!(
         bool, "flag1",    1,
         bool, "flag2",    1,
         uint, "",         6));
 }

 Is this inside a function? If so, put `static` on it.

 What you are seeing is the 8-byte frame pointer that comes from 
 inner structs so you can access stack variables inside the 
 struct.

 -Steve

It was run on the doc page. I suppose the examples are wrapped in 
a unittest block?

Anyways, I appreciate your explanation.

MoonlightSentinel <moonlightsentinel disroot.org> writes:

On Tuesday, 28 July 2020 at 09:28:27 UTC, wjoe wrote:
 It was run on the doc page. I suppose the examples are wrapped 
 in a unittest block?

Indeed, see 
https://github.com/dlang/phobos/blob/cd2ba0d2c378a893ec0eaefc57b87d0770a1990c/std/bitmanip.d#L293-L314

wjoe <invalid example.com> writes:

On Tuesday, 28 July 2020 at 09:46:01 UTC, MoonlightSentinel wrote:
 On Tuesday, 28 July 2020 at 09:28:27 UTC, wjoe wrote:
 It was run on the doc page. I suppose the examples are wrapped 
 in a unittest block?

 Indeed, see 
 https://github.com/dlang/phobos/blob/cd2ba0d2c378a893ec0eaefc57b87d0770a1990c/std/bitmanip.d#L293-L314

Thank you.

Steven Schveighoffer <schveiguy gmail.com> writes:

On 7/28/20 5:46 AM, MoonlightSentinel wrote:
 On Tuesday, 28 July 2020 at 09:28:27 UTC, wjoe wrote:
 It was run on the doc page. I suppose the examples are wrapped in a 
 unittest block?

 
 Indeed, see 
 https://github.com/dlang/phobos/blob/cd2ba0d2c378a893ec0eaefc57b87d0770a1990c/std/
itmanip.d#L293-L314 
 

It doesn't necessarily need to be in a unittest block (AFAIK, the 
example executer isn't actually running the unittests of phobos), but it 
does need to be inside a function, because you have executable code 
there. Either way, yes, it's run inside a function, so you need to apply 
static to the struct to avoid the frame pointer. I tested that, and it 
prints 1 instead of 16.

-Steve

wjoe <invalid example.com> writes:

On Tuesday, 28 July 2020 at 13:00:12 UTC, Steven Schveighoffer 
wrote:
 On 7/28/20 5:46 AM, MoonlightSentinel wrote:
 On Tuesday, 28 July 2020 at 09:28:27 UTC, wjoe wrote:
 It was run on the doc page. I suppose the examples are 
 wrapped in a unittest block?

 
 Indeed, see 
 https://github.com/dlang/phobos/blob/cd2ba0d2c378a893ec0eaefc57b87d0770a1990c/std/bitmanip.d#L293-L314
 

 It doesn't necessarily need to be in a unittest block (AFAIK, 
 the example executer isn't actually running the unittests of 
 phobos), but it does need to be inside a function, because you 
 have executable code there. Either way, yes, it's run inside a 
 function, so you need to apply static to the struct to avoid 
 the frame pointer. I tested that, and it prints 1 instead of 16.

 -Steve

My reasoning was that a unittest is essentially a function and 
it's incredibly convenient for such things but I hadn't really 
checked prior to MoonlightSentinel's reply.

Thanks again :)