Opaque structs

[Johannes Pfau]

Am Sat, 29 Jun 2013 10:54:32 +0200
schrieb "Maxim Fomin" <maxim at maxim-fomin.ru>:

> On Saturday, 29 June 2013 at 08:01:17 UTC, Johannes Pfau wrote:
> > Am Fri, 28 Jun 2013 22:16:33 +0200
> > schrieb Andrej Mitrovic <andrej.mitrovich at gmail.com>:
> >
> >> On 6/28/13, Johannes Pfau <nospam at example.com> wrote:
> >> > A naive question: Why isn't struct S {} enough? This should 
> >> > be a
> >> > struct with size 0 so why do we need to disable the 
> >> > constructor and
> >> > postblit explicitly?
> >> 
> >> Because the user should never be able to use such a struct by 
> >> value,
> >> in other words a user might mistakenly write code such as:
> >> 
> >>     S s2 = *s;  // copies 1 byte
> >
> > But why is that legal / does that copy _one_ byte? It seems 
> > like that's
> > totally arbitrary. Shouldn't doing anything value-related on
> > an empty struct be invalid anyway?
> 
> It copies one byte because empty structs have one byte - 
> according to D implementation. The value can be adjusted using 
> align() atrribute.

I see. I didn't know that we have this in the spec, but I guess there's
some good reason for this behavior if it was explicitly specified /
implemented.