Optimal struct layout template?

[Andrei Alexandrescu]

BCS wrote:
> Reply to dsimcha,
> 
>> According to the spec, data stored in structs is guaranteed to be laid
>> out in the order specified in the source code.  While this is
>> necessary in some low-level code, I have a use case where I need to
>> pack structs as efficiently as possible.  These structs are to be
>> stored in an array, and for efficiency reasons I want to store them
>> directly rather than storing pointers, so using classes is out of the
>> question.  Does anyone know how to write a template that, given a
>> tuple of types, will reorder the tuple so that it will produce the
>> optimal struct layout?  I don't care, at least for now, if it assumes
>> x86-32/DMD instead of handling the more general case.
>>
> 
> would "align 1" work?

That could make things excruciatingly slow. What's really needed is (in 
first approximation) to sort the members in decreasing order of size. 
Odd-sized arrays of char foil this plan to some extent, which is where 
the fun begins.

Andrei