Re: [boost] Re: New version of valunion and stack_allocator uploaded

From: David Abrahams (david.abrahams_at_[hidden])
Date: 2002-03-01 09:06:56

----- Original Message -----
From: "Douglas Gregor" <gregod_at_[hidden]>

> On Thursday 28 February 2002 05:27 pm, you wrote:
> > > I did something like that at one point, and it was painful to
compiler. I
> > > like Brian Parker's version because it is so much simpler than any
> > > typelist-based approach.
> >
> > Can you give the quick one-sentence summary of what he's doing?
>
> The type to align against is a union, where the type 'X' of each member is
a
> type 'U' if sizeof(U) <= sizeof(type_we_want_to_make_storage_for) and char
> otherwise.

So if the type I'm storing is char[6], it will over-align, yes?

In my application it's much more important to actually produce an
appropriate alignment than that the size is minimal, but that won't be true
for many. Since this is all a crapshoot anyway and the language gives no
guarantees of success it seems like Brian's algorithm ought at least to
check that sizeof(U) <= alignment_of(type_we_want_to_make_storage_for).

-Dave