I am trying to port a serialization library I wrote in Lua some time ago. I've ran into a problem relating to types with anonymous unions inside.

Given this code:
enum Kind
{
   none = 0,
   array,
   integer,
   floating,
}

struct Foo
{
   Kind type;
   union
   {
       ulong  integer;
       double floating;
       void[] array;
   }
   int nonUnionField;
   //...
}

How can I tell that "integer", "floating" and "array" are part the union while "nonUnionField" is not?

Thanks in advance.

On 21/10/2016 8:55 PM, TheFlyingFiddle wrote:
> I am trying to port a serialization library I wrote in Lua some time
> ago. I've ran into a problem relating to types with anonymous unions
> inside.
>
> Given this code:
> enum Kind
> {
>    none = 0,
>    array,
>    integer,
>    floating,
> }
>
> struct Foo
> {
>    Kind type;
>    union
>    {
>        ulong  integer;
>        double floating;
>        void[] array;
>    }
>    int nonUnionField;
>    //...
> }
>
> How can I tell that "integer", "floating" and "array" are part the union
> while "nonUnionField" is not?
>
> Thanks in advance.

You're gonna have to use UDA's for that.

On Friday, 21 October 2016 at 07:56:27 UTC, rikki cattermole wrote:
> You're gonna have to use UDA's for that.

Yes, to do the serialization you're right.

But my usecase for this is for error reporting. Basically any struct that contains unions without serialization instructions cannot be serialized and I want to make such structures errors.

So when I try to serialize the example struct Foo. It should assert with something along the lines of:

"Don't know how to serialize overlapping fields: "Foo.integer", "Foo.floating" and "Foo.array".

On 21/10/2016 9:13 PM, TheFlyingFiddle wrote:
> On Friday, 21 October 2016 at 07:56:27 UTC, rikki cattermole wrote:
>> You're gonna have to use UDA's for that.
>
> Yes, to do the serialization you're right.
>
> But my usecase for this is for error reporting. Basically any struct
> that contains unions without serialization instructions cannot be
> serialized and I want to make such structures errors.
>
> So when I try to serialize the example struct Foo. It should assert with
> something along the lines of:
>
> "Don't know how to serialize overlapping fields: "Foo.integer",
> "Foo.floating" and "Foo.array".

I suppose you could use .offsetof to determine this.

On Friday, 21 October 2016 at 08:18:58 UTC, rikki cattermole wrote:
> On 21/10/2016 9:13 PM, TheFlyingFiddle wrote:
>> On Friday, 21 October 2016 at 07:56:27 UTC, rikki cattermole wrote:
>>> You're gonna have to use UDA's for that.
>>
>> Yes, to do the serialization you're right.
>>
>> But my usecase for this is for error reporting. Basically any struct
>> that contains unions without serialization instructions cannot be
>> serialized and I want to make such structures errors.
>>
>> So when I try to serialize the example struct Foo. It should assert with
>> something along the lines of:
>>
>> "Don't know how to serialize overlapping fields: "Foo.integer",
>> "Foo.floating" and "Foo.array".
>
> I suppose you could use .offsetof to determine this.

This is what I was looking for. Thanks!