Re: [boost] Review request for Boost.Align

On Thu, Feb 20, 2014 at 7:07 PM, Peter Dimov wrote:

Andrey Semashev wrote:

...

this will likely not work because std::list won't use my_alignment_of<__m128 > but instead some my_alignment_of< list_node< __m128

...

...

. To make this work you'd have to write some fake metafunction that just always returns 64, and this is equivalent to just specifying 64 in aligned_allocator template parameters, only more complicated.

Specifying 64 is not going to work for list<> containers. That was my point.

template< class T > struct __list_node { void* next_; T t_; }

If you align the __list_node at 64, the t_ member is not going to be aligned at 64.

aligned_allocator is going to work for vector<> though, and this is often precisely what's needed. So I think that your suggestion of specifying a minimal alignment, with the actual alignment being determined as LCM( min_align, alignof(T) ) is useful, as long as people realize that it's tailored to vector<> and is not generally suitable.

You're right, I forgot about the node layout. I guess, the only way to make sure it works in all cases is to use both the element type with the required alignment and aligned_allocator.