Emulating enums

[Ali Çehreli]

On 07/31/2013 06:10 PM, JS wrote:
> http://dpaste.dzfl.pl/dbb40dbc
>
> The code was pared down from a lot of string mixin code generation. I
> nest the structs because I want a nested enums. I don't want have to
> have eState and eStateType but eState and eState.Type.
>
> Having the ability to nest enums would solve my problem.
>
> Regardless, I can almost achieve the effect with nested structs but not
> quite.
>
> In the code, I cannot assign to the struct for some reason even with
> alias this on iB, which should make State act like the int Value.
>
> i.e.,
>
> b.State.Value = Enums.State.A;
>
> works but
>
> b.State = Enums.State.A;
>
> doesn't
>
> It maybe some stupid error on my part but I can't keep my eyes open
> enough to figure it out...
>
>
>

For that assignment to work, the left-hand side must be assignable. 
However, the property function State() returns Enums.eState by-value.

The following has the same issue:

struct S
{
     int i_;

     @property int i() {
         return i_;
     }

     alias i this;
}

void main()
{
     auto s = S();
     s = 42;
     assert(s.i == 42);
}

Error: cannot implicitly convert expression (42) of type int to S

To compile, i() must return an lvalue:

     @property ref int i() {

Ali