Opaque structs

[Johannes Pfau]

Am Sat, 29 Jun 2013 17:38:38 +0200
schrieb "monarch_dodra" <monarchdodra at gmail.com>:

> On Saturday, 29 June 2013 at 08:01:17 UTC, Johannes Pfau wrote:
> > Shouldn't doing anything value-related on
> > an empty struct be invalid anyway?
> 
> Why ?
> 
> The fact that the struct has no members is an implementation 
> detail which should have no impact on the user of the struct.

It's probably a matter of perception. As you said in your other post
there are good reasons to give empty structs a size. But if you
(naively) think of a struct as a simple aggregate of other types, then a
aggregate of zero other types should have size zero. There's no
information in such a struct which would have to take up space. And
doing something value-related on some type which doesn't have a size
and therefore doesn't have a value is not really well-defined. (How do
you copy a value of size 0? What happens if you dereference a pointer
to a value of size 0?).