Re: [boost] [function] Placement new warnings from gcc 6

Subject: Re: [boost] [function] Placement new warnings from gcc 6
From: Andrey Semashev (andrey.semashev_at_[hidden])
Date: 2016-04-03 16:36:43

On 2016-04-03 14:39, Larry Evans wrote:
> On 04/02/2016 08:08 AM, Andrey Semashev wrote:
> [snip]
>>   union function_buffer
>>   {
>>     mutable function_buffer_members m;
>>     mutable char data[sizeof(function_buffer_members)];
>>   };
>>
>> This would require more modifications to the code though.
>>
>> (Sigh... if only we could inherit unions...)
>>
>
> Could you provide an example of how you'd like to inherit unions?
> I'm guessing:
>
>   union function_buffer
>   : supertype_1
>   , supertype_2
>     ...
>   , supertype_N
>   {
>   };
>
> where all of the supertype_I's would occupy the same storage?

Yes. More precisely, all supertype_I's and function_buffer's members 
would map to the same storage, and supertype_I's members would be 
syntactically addressed as if those were members of function_buffer 
(i.e. similarly how it is with structs and classes).

The above function_buffer definition could be written as:

   union function_buffer : public function_buffer_base
   {
     mutable char data[sizeof(function_buffer_base)];
   };

and members of function_buffer and function_buffer_base could be 
addressed similarly:

   function_buffer fb;
   fb.obj_ptr = ...;
   fb.data = ...;