What should happen here?

[Walter Bright]

On 9/20/2021 11:26 AM, Steven Schveighoffer wrote:
> [...]

1, 2, or 3 are all valid outcomes.

The lifetime of a GC allocated object ends when there are no longer live 
references to it. Live references can end before the scope ends, this is called 
"non-lexical scoping". That does not imply that that is when the class 
destructor is run. The class destructor runs at some arbitrary time *after* 
there are no longer references to it.

The GC is not obligated to run a collection cycle upon program termination (a 
laxity intended to improve shutdown performance), and hence it is not obliged to 
run the class destructors.

The inevitable consequence of this is:

Do *not* use the GC to manage non-memory resources.

But if you must do it anyway, use the "destroy" and "free" GC special functions. 
Of course, if you decide to use these functions, it's up to you to ensure 
resources are free'd exactly once.

https://dlang.org/phobos/object.html#.destroy
https://dlang.org/phobos/core_memory.html#.GC.free

P.S. A live reference is one where there is a future use of it. A dead reference 
is one where there isn't a future use. The `c` variable is a dead reference 
immediately after it is initialized, which is why optimizers delete the 
assignment. The `new C` return value is dead as soon as it is created.

P.P.S. Attempting to deduce the GC's rules from observing its behavior is very 
likely a path to frustration and errors, because its observed behavior will not 
make sense (and will appear random) unless one understands the above explanation.

P.P.S. Do not conflate class destructors with struct destructors. The latter 
follow RAII rules, the former does not.