[Dlang-study] [lifetime] Few root decisions to take on RC classes

[Marc Schütz]

On Friday, 6 November 2015 at 02:44:39 UTC, Michel Fortin wrote:
> But how do you prevent the payload from being leaked in a way 
> that it outlives the droppable? For instance, someone might 
> want to log the exception message and put it into a queue for a 
> separate logging thread to process. You're giving raw access to 
> the string, so it's very easy mess things up if you are not 
> careful.

Well, that requires borrowing/sealed references:

struct Droppable(T) {
     private T payload;
     void delegate(ref T object) dropper;
     ref T borrow() return { return payload; }
     alias borrow this;
     @disabled this(this);
     ~this() {
         if(dropper) dropper(payload);
     }
}

But that's a separate topic. My point was that this is a 
mechanism to abstract away from specific ownership schemes 
without making the ownership part of the type (i.e. `Exception` 
can be used as-is no matter whether the message if garbage 
collected or refcounted or static).