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)                                                                       
{                                                                                                                          
    switch(s){                                                                                                             
    case "low":                                                                                                            
        return Quality(Low());                                                                                                                                                                                                          
    case "high":                                                                                                           
        return  Quality(High());                                                                                                                                                                                                        
    case "medium":                                                                                                         
        return Quality(Medium());                                                                                                                                                                                                       
    case "original":                                                                                                       
        return Quality(Original());                                                                                        
    default:                                                                                                               
        assert(false);                                                                                                         
    }                                                                                                                      
}   

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