Thread overview
variant .init value
Feb 07
Norm
Feb 07
Alex
Feb 07
Norm
Feb 07
bauss
February 07
Hi,

I'm trying to use Variant in a struct and want a default init value like so:

---
struct S {
  Variant v = Variant(10);
}
void main() {auto s = S();}

but when I try to build this I get the following error:

dmd2/linux/bin64/../../src/phobos/std/variant.d(661): Error: memcpy cannot be interpreted at compile time, because it has no available source code
Error: cannot interpret <error> at compile time
---

I don't particularly need or want this to be available at compile time, I really only want the struct to have a default value when instantiated at runtime.

Is there a way to do this with a Variant member?

Thanks,
Norm
February 07
On Thursday, 7 February 2019 at 07:33:50 UTC, Norm wrote:
> Hi,
>
> I'm trying to use Variant in a struct and want a default init value like so:
>
> ---
> struct S {
>   Variant v = Variant(10);
> }
> void main() {auto s = S();}
>
> but when I try to build this I get the following error:
>
> dmd2/linux/bin64/../../src/phobos/std/variant.d(661): Error: memcpy cannot be interpreted at compile time, because it has no available source code
> Error: cannot interpret <error> at compile time
> ---
>
> I don't particularly need or want this to be available at compile time, I really only want the struct to have a default value when instantiated at runtime.
>
> Is there a way to do this with a Variant member?
>
> Thanks,
> Norm

Hmm... found something similar from 2014...
https://issues.dlang.org/show_bug.cgi?id=11864
February 07
On Thursday, 7 February 2019 at 07:44:17 UTC, Alex wrote:
> On Thursday, 7 February 2019 at 07:33:50 UTC, Norm wrote:
>> [...]
>
> Hmm... found something similar from 2014...
> https://issues.dlang.org/show_bug.cgi?id=11864

Thanks, I've added a comment to that bug report.

Cheers,
Norm
February 07
On Thursday, 7 February 2019 at 07:33:50 UTC, Norm wrote:
> Hi,
>
> I'm trying to use Variant in a struct and want a default init value like so:
>
> ---
> struct S {
>   Variant v = Variant(10);
> }
> void main() {auto s = S();}
>
> but when I try to build this I get the following error:
>
> dmd2/linux/bin64/../../src/phobos/std/variant.d(661): Error: memcpy cannot be interpreted at compile time, because it has no available source code
> Error: cannot interpret <error> at compile time
> ---
>
> I don't particularly need or want this to be available at compile time, I really only want the struct to have a default value when instantiated at runtime.
>
> Is there a way to do this with a Variant member?
>
> Thanks,
> Norm

I know this is not ideal, but here is a "workaround":

struct S {
  Variant v;

  static S opCall()
  {
      S s;
      s.v = Variant(10);
      return s;
  }
}

Would have worked better if structs allowed default ctor in D, but they don't unfortunately.