class Default : Object {                                                        
    public string default_id { owned get; construct; default = "default"; }     
    public int val { get; construct; }                                          
}                                                                               
                                                                                
class Derived : Default {                                                       
    public Derived() {                                                          
        Object (val: -1);                                                       
    }                                                                           
                                                                                
    public void do_something () {                                               
        print ("Default: %s\n", this.default_id);                               
    }                                                                           
}                                                                               
                                                                                
int main (string[] args) {                                                      
    var d = new Derived ();                                                     
                                                                                
    d.do_something ();                                                          
                                                                                
    return 0;                                                                   
}          

Output:
 ./default 
Default: (null)