About ref used for performance reasons with struct

[deadalnix]

On Monday, 11 February 2013 at 23:16:55 UTC, Peter Alexander 
wrote:
> On Monday, 11 February 2013 at 06:52:33 UTC, deadalnix wrote:
>> I'm thinking about it for a while now and I'm now convinced 
>> that we should allow the compiler to do that job for us. Let 
>> me explain.
>
> struct Foo { int x, y; }
>
> class Bar
> {
>     Foo[] foos = [Foo(1, 2)];
>
>     void swap(const(Foo) f)
>     {
>         foos[0].x = f.y;
>         foos[0].y = f.x;
>     }
> }
>
> void quux(Bar bar, const(Foo) foo)
> {
>     bar.swap(foo);
> }
>
> Are the foo parameters allowed to be passed by ref in both 
> these functions? I see no reason why not from your criteria, 
> but doing so changes the program.

I guess the constraint are too lax. Is it possible to get around 
that without creating a cascade of special cases ? I frankly 
don't know, I have to dig more into this.