Opaque structs

[Maxim Fomin]

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.