Destroying structs without a typeinfo object

[Steven Schveighoffer]

On Fri, 04 May 2012 08:38:21 -0400, Benjamin Thaut  
<code at benjamin-thaut.de> wrote:

> Am 04.05.2012 14:18, schrieb Steven Schveighoffer:
>> On Fri, 04 May 2012 02:45:03 -0400, Benjamin Thaut
>> <code at benjamin-thaut.de> wrote:
>>
>>> Hi,
>>>
>>> I'm currently doing some manual memory management and as the delete
>>> keyword is deperecated I want to replace it with a custom Delete
>>> template. I now need to destroy a array of structs, this however seems
>>> only be possible by using the typeinfo object of the struct and
>>> calling xdtor on that which is a indirect function call for every
>>> struct in the array. I would like to destroy the struct directly with
>>> a direct call to the destructor. This seems not to be possible because
>>> calling __dtor results in calling the wrong dtor (apperently there are
>>> 3, __dtor, __fieldDtor, __aggrDtor). So __dtor is the wrong destructor
>>> because it does not destroy any members of the struct but __fieldDtor
>>> and __aggrDtor are not callable. They show up in the
>>> __traits(allMembers) list but if you try to call them you get a error
>>> message that such a property does not exist. So is there any way to
>>> directly destroy a struct, and if not why can't we directly expose the
>>> correct destructor, because apprently it is known at compile time.
>>
>> Look at what object.clear() does, since it is meant to replace delete.
>>
>> In fact, I'd advise just using that if you have the type handy.
>>
>> -Steve
>
> object.clear() useses the typeinfo.destroy() method which is a virtual  
> function call plus a indirect function call. So thats even one level of  
> indirection more. Also clear does reinitializle the struct after  
> destroying it, which is completely unneccesary in my case, because I'm  
> about to free the memory anyway.

Look at what TypeInfo_Struct.destroy() does:

     override void destroy(void* p)
     {
         if (xdtor)
             (*xdtor)(p);
     }

So here is what I'd suggest (for an array of struct S):

auto ti = typeid(S).xdtor;

if(xdtor)
   foreach(ref s; arr)
      (*xdtor)(&s);

Which should be as efficient as possible, given the current  
implementation, you don't have to repeat the lookup for each element.

I remember that __dtor does the wrong thing, and I advocated it should do  
the same thing as calling xdtor, but it didn't go anywhere.

-Steve