Sense check: construction / deconstruction

[Jordan Wilson]

On Tuesday, 24 April 2018 at 23:49:14 UTC, Steven Schveighoffer 
wrote:
> What you are missing is that Database is pass-by-value, not a 
> class. So when you include it directly in a class like you did 
> in A, then when A's destructor is called, db's destructor is 
> called.
>
> Since in the first case, a is being destroyed by the GC, you 
> get the error.

Ok, this makes sense.

> In the second case (b), you aren't including the db by value, 
> so no destructor is called from the GC. But this is dangerous, 
> because db stops existing after main exits, but b continues to 
> exist in the GC, so this is a dangling pointer.

If I set the pointer to null, before (b) is collected, would that 
work?

> In the third case, scoped specifically destroys c when main 
> exits, and you are not in the GC at that point.
>
> What the error message is telling you is you should manually 
> clean up the database directly instead of leaving it to the GC. 
> What is the correct path? probably the scoped!A version. Though 
> I'm not sure what making copies of the database does in that 
> library.
>
> -Steve

Ok I'll need to read the docs on scoped I think, but I think I 
understand.

If I wanted db to be persistent, but have temporary objects 
reference db without triggering GC collection of the db, you 
would use scoped?
Or is this a situation where it's better to pass the db in 
function calls to objects rather than set as a member of these 
objects?