Re: Why are std.bitmanip.bitfields so big ?
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 :)
Re: Why are std.bitmanip.bitfields so big ?
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
Re: Why are std.bitmanip.bitfields so big ?
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.
Re: Why are std.bitmanip.bitfields so big ?
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
Re: Why are std.bitmanip.bitfields so big ?
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.
Re: Why are std.bitmanip.bitfields so big ?
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
Why are std.bitmanip.bitfields so big ?
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
