Delegate is left with a destroyed stack object

[Peter Alexander]

On Wednesday, 30 October 2013 at 09:20:40 UTC, Lionello Lunesu 
wrote:
> On 10/29/13, 22:42, David Nadlinger wrote:
>> On Tuesday, 29 October 2013 at 21:41:25 UTC, Lionello Lunesu 
>> wrote:
>>> So a copy should have been made of the live object, not the 
>>> destructed
>>> one. Correct?
>>
>> No. There should only be one struct instance, the one living 
>> (forever)
>> in the closure context.
>>
>> David
>
> Why? It's a struct. It should be completely fine to create a 
> copy [on the heap] for the closure context.

That would be worse:

void increment(ref int x) { ++x; }

void run(void delegate() f) { f(); }

void main()
{
     int x = 0;
     run( { increment(x); } );
     writeln(x);
}

If the closure took a copy of x then this would write 0. 
Certainly not what I would expect.

I think not running the destructor is the best option (although 
to be honest, I'm not a huge fan of closures to begin with, for 
exactly these sorts of reasons -- they only really work well in a 
pure functional setting).