Optional type - how to correctly reset a wrapped immutable T

[jmh530]

On Tuesday, 27 March 2018 at 13:51:20 UTC, jmh530 wrote:
> 
>
> How about:
> [snip]

I can kind of like this more, but after re-reading your original 
post I'm not sure it really resolves your issue:

struct Optional(T) {
     import std.traits : isMutable;
     T[] bag;

     this(T t) inout {
         bag = [t];
     }

     void opAssign(T rhs)
     {
         static if (isMutable!T)
             bag[0] = rhs;
         else
             bag = [rhs];
     }
}

Optional!T optional(T)(T x)
{
     return Optional!T(x);
}

void main()
{
     int x = 3;
     const(int) xx = 3;
     immutable(int) xxx = 3;
     immutable(int) xxxx = 4;

     auto y = optional(x);
     auto yy = optional(xx);
     auto yyy = optional(xxx);
     yyy = xxxx;
}