Implicit conversion of struct to bool for if (s) operation ?

[chmike via Digitalmars-d-learn]

Hello,

I have a structure with two fields ad defined as

struct Info {
     this(int value, Category category)
     {
         category_ = category;
         value_ = category ? value : 0;
     }
     ...
private:
     Category category_ = null;
     int value_ = 0;
}


I would like an implicit conversion of Info to bool that return 
false if category_ is null so that I can write

Info s = foo();
if (s) {
    ...
}

and where

Info s2;
assert(!s2);