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December 09, 2012
rtInfo issue
I'm currently using the rtInfo template inside object.d to generate RTTI 
information for my own little rtti system. It is working really well so 
far, the only issue I found is as follows:

If a POD struct (which does not contain any reference types, pointers, 
arrays etc) is placed in a library. And that library is then linked 
against a executable, the rtInfo of the POD struct will be lost. It will 
be generated by the compiler when compiling the library, but for some 
reason it is gone after the final binary is compiled and linked. But as 
soon as I add a void* pointer to that struct everythings works fine.

Any idea what could be happening there and how to fix it? If the linker 
stripts the rtInfo out, why does adding a void* make a difference?

The source can be found at:

https://github.com/Ingrater/druntime/blob/master/src/rtti.d
https://github.com/Ingrater/druntime/blob/master/src/object.di

Kind Regards
Benjamin Thaut
December 09, 2012
Re: rtInfo issue
On 12/9/2012 11:36 AM, Benjamin Thaut wrote:
> If a POD struct (which does not contain any reference types, pointers, arrays
> etc) is placed in a library. And that library is then linked against a
> executable, the rtInfo of the POD struct will be lost. It will be generated by
> the compiler when compiling the library, but for some reason it is gone after
> the final binary is compiled and linked. But as soon as I add a void* pointer to
> that struct everythings works fine.
>
> Any idea what could be happening there and how to fix it? If the linker stripts
> the rtInfo out, why does adding a void* make a difference?


Template instances are written to COMDAT sections, which are stripped out if 
they are not referenced.
December 09, 2012
Re: rtInfo issue
Am 09.12.2012 21:22, schrieb Walter Bright:>
>
> Template instances are written to COMDAT sections, which are stripped
> out if they are not referenced.
>

But why does adding a void* pointer make a difference then? By adding a 
void* pointer to the struct it will still not be referenced

Before (broken):

struct Pod { float x; }

After (working):

struct Pod { float x; void* ptr; }

Kind Regards
Benjamin Thaut
December 09, 2012
Re: rtInfo issue
Ok I tried to manually reference it, it does not help.

struct Quaternion {
	float x,y,z,angle;
}

class ForceReference
{
  Quaternion q;
}

shared static this()
{
  Quaternion q;
  auto t = typeid(Quaternion);
  auto info = RTInfo!Quaternion;
  printf("%x %x\n", info, t.rtInfo);
}

Although info is not null t.rtInfo is null.

Kind Regards
Benjamin Thaut
December 09, 2012
Re: rtInfo issue
On 12/9/2012 12:28 PM, Benjamin Thaut wrote:
> But why does adding a void* pointer make a difference then? By adding a void*
> pointer to the struct it will still not be referenced
>
> Before (broken):
>
> struct Pod { float x; }
>
> After (working):
>
> struct Pod { float x; void* ptr; }

I suggest looking at the difference between the object files for the two cases.
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