On Sunday, 26 September 2021 at 13:29:26 UTC, Paul Backus wrote:
> On Sunday, 26 September 2021 at 07:49:46 UTC, Daniel N wrote:
>> // I hope this works, otherwise it violates the 'law of least surprise'
>> auto c = new Class()
>> scope(exit) destroy(c);
>>
>> If scope(exit) also works, then I don't think there is any problem...
>
> Destroy on a class reference doesn't call the destructor; it just sets the reference to null.

Correction: I remembered wrong; it actually does call the destructor. So this will work for classes with non-trivial destructors.

On Sat, Sep 25, 2021 at 07:13:50PM -0700, Walter Bright via Digitalmars-d wrote:
> On 9/25/2021 6:02 PM, Steven Schveighoffer wrote:
> > As I said, the optimizer is fighting you the entire way.
> 
> I'd reframe it as the user is trying to impose his own semantics on the optimizer :-)

IMO, those are just the symptoms.

The core of the problem is that we failed to inform the GC of a reference to some object (because said reference was passed into C land and no longer exists in D land).

GC.addRoot is precisely the ticket that solves this core issue: it informs the GC about said reference. **This is what addRoot is for.**

All the other elaborate attempts to "fix" this problem without using GC.addRoot is just skirting around the issue without actually addressing the problem.  No wonder it feels likes "the optimizer is fighting you the entire way."  Actually, the optimizer is NOT trying to fight you; it's merely telling you that **the semantics expressed in your code is not what you think it is**.  It's simply reducing your code to its actual semantics as defined by the specs. The fact that this reduction isn't what you expect is a sign that the original code doesn't actually mean what you think it means.

It's like trying to prevent a boolean expression from reducing to a constant value by adding more clauses to it.  If there's already a tautology in your expression, it's not gonna change no matter what else you try to add to it.  Fix the tautology, and all of the problems go away. There's no need for all the other fluff.

Seriously, guys, just use GC.addRoot. **That's what it's for.**  Stop trying to cure cancer with Tylenol already! :-D


[...]
> > But I still am wishing for a simple "keep this alive" mechanism that doesn't add too much cruft, and is guaranteed to keep it alive.
> 
> That's exactly what addRoot() is for.

If calling addRoot causing "performance problems" (or whatever other objections one may raise), we can look into improving its performance in various ways. But avoiding to call it in the first place is not a solution.


T

-- 
"Computer Science is no more about computers than astronomy is about telescopes." -- E.W. Dijkstra