Delegate is left with a destroyed stack object

[David Nadlinger]

On Tuesday, 29 October 2013 at 21:14:39 UTC, qznc wrote:
> { writeln(s); } // creates closure with reference to stack 
> memory "&s"
> return ... // returns and destroys local variable s, i is now 
> 666
> foo()() // calls closure with reference to invalid memory "&s"

That's not how closures work in D – the local variables 
referenced by nested functions/closures will be allocated inside 
the "nested context" for the function, which is placed on the GC 
heap if a reference to it can be escaped. Play around with the 
example some more if you want: Barring any further DMD bugs, you 
are not going to get the contents of i to be corrupted (i.e. set 
to another garbage value).

The problem with the compiler behavior for the code in question 
is that it destructs a live object, and thus clearly breaks the 
type system.

I think the only correct resolution is to not destruct the object 
at the end of foo() – which incidentally also means that the 
destructor will never be invoked, just as for any other 
GC-finalized memory.

David