[Bug c++/15795] No way to teach operator new anything about alignment requirements

["jason at redhat dot com" <gcc-bugzilla@gcc.gnu.org>]

------- Additional Comments From jason at redhat dot com  2004-06-08 20:04 -------
Subject: Re:  No way to teach operator new anything about
 alignment requirements

On 8 Jun 2004 19:25:27 -0000, "bangerth at dealii dot org" <gcc-bugzilla@gcc.gnu.org> wrote:

> I we are to provide a workaround, I think that the signature you 
> propose, i.e. 
>   operator new (size_t size, enum align_tag, size_t align); 
> may not be a good idea, the second and third argument being an integer.  This 
> is just way too common and asking for trouble.

I don't think it would actually be a problem, since enums are distinct
types.  But I understand your concern, since they do promote to integers,
and I'm not opposed to using a struct instead.

> Having something like 
>   template <int> struct Alignment {}; 
>   template <int N> operator new (size_t, Alignment<N>); 

Or

template <typename T> struct Alignment
{
  static const size_t alignment = __alignof (T);
};
template <typename T> inline void *
operator new (size_t size, Alignment<T> align)
{
  return align_new (size, align.alignment);
}

...
new (Alignment<Vector4>) Vector4[200];

Yes, that seems like a cleaner syntax for explicit placement new.

> may also be a neat possibility if we use SFINAE to provide  
>   template <int N> 
>   typename SFINAE<(N<=STD_ALIGNMENT),void*> operator new (size_t,Alignment<T>) 
> and the opposite case as two overloads, and let the compiler pick which  
> one it wants to call. This way we can switch at compile time which allocation 
> function shall be called. But I think I'm carried away... ;-) 

I'm not familiar with SFINAE.

Jason


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=15795