More magical AA semantics

[Jens Mueller]

Don wrote:
> Consider this code:
> ---
>    int[int] x;
> 
>    int k = x[2] + 5; // Error, range violation. Makes sense.
> 
>    x[2] = x[2] + 5;  // But this works!!!
> ---

I think the last statement is illegal. Because from
http://dlang.org/expression.html I extract:

The evaluation order of = is implementation defined and it is illegal to
depend on it. The compiler should catch these but it cannot in all
cases. If the evaluation order was fixed i.e. right-to-left in this
case, the code would throw. It also happens that the evaluation may
change depending on the optimization flags.
So I believe it's an issue of evaluation order.

Jens