Optional and NotNull version 0.5.0 - swift optional like and scala option like

[Paul Backus]

On Friday, 24 August 2018 at 20:59:34 UTC, aliak wrote:
> THis is true. And might be interesting to try out actually. Can 
> you access the types in a SumType via index?
>
> I'm thinking because Optional behaves like a range, and I guess 
> I'd define a SumType!(T, None), then a rough outline may be:
>
> struct None {}
> immutable none = None();
>
> struct(T) {
>   SumType(T, None) opt;
>   T front() {
>     return opt[0]; // what to do here?
>   }
> }
>
> Or I guess I should maybe do it like this?:
>
> return opt.match!(
>   (T val) => val,
>   (None) => T.init,
> );

I think this is probably the best way:

@property T front() {
     return opt.match!(
         (T val) => val,
         (None) {
             assert(false, "called .front on an empty range");
             return T.init; // for return type inference
         }
     );
}

You could also do it with `tryMatch` and 
`std.exception.assertNotThrown`. It makes the code a little 
nicer, but involving exceptions at all seemed like unnecessary 
overhead to me.