Code shared from run.dlang.io.

main.d

/+dub.sdl:
dependency "sumtype" version="~>0.8.11"
+/
import std.stdio;
import sumtype;
struct High {}
struct Low{}
struct Medium{}
struct Original{}
struct None{};
alias Quality = SumType!(High, Medium, Low, Original);

@safe pure Quality asQEnum(string s)
{
    Quality q;
    switch(s){
    case "low":
        q = Low(); break;
    case "high":
        q = High(); break;
    case "medium":
        q = Medium(); break;
    case "original":
        q = Original(); break;
    default:
        assert(false);
    }
    return q;
}

void main(){
    writeln("high".asQEnum);
}