Remaining const niggles #1 - Custom POD types

[Walter Bright]

Janice Caron wrote:
> The problem is that the
> following /doesn't/ work (as in, won't compile!)
> 
>     typedef char mychar;
>     alias invariant(mychar)[] mystring;
> 
>     mystring s = cast(mystring)"hello";
>     mychar c = s[0];

That's a bug and will get fixed on the next update. The rule is that a 
typedef can be implicitly converted to/from invariant if the underlying 
type can be.

Structs will be implicitly convertible to/from invariant if each of its 
fields can be (even private fields).