Why is the struct instance being copied here?

[Steven Schveighoffer]

On Fri, 11 Mar 2011 04:50:38 -0500, d coder <dlang.coder at gmail.com> wrote:

> Greetings
>
> Please look at the code down here. When compiled and run, I get the  
> message
> "Call to postblit" printed. I think it is because of the foreach block,
> because the variable "i" is not declared as ref there. Is there a way to
> make it a ref?
>
> Regards
> - Puneet
>
> import std.stdio;
>
> struct Foo {
>   this(this) {
>     writeln("Call to postblit");
>   }
> }
>
> class Bar {
>   Foo foo;
>   this() {
>     foreach(i, f; this.tupleof) {
>       // do nothing
>     }
>   }
> }
>
> void main()
> {
>   Bar bar = new Bar();
> }

This typically works in a foreach loop:

foreach(i, ref f; x)

but a foreach for a tuple is a special beast, and using ref in your code  
yields this error:

foreachtuple.d(12): Error: no storage class for value f

But I agree it should be doable.  This should qualify for an enhancement  
request: http://d.puremagic.com/issues/enter_bug.cgi?product=D

-Steve