TDPL: Manual invocation of destructor

[bearophile]

Steven Schveighoffer:
> The thing is, even with clear, the above code is undefined -- a cleared  
> object is in no state to be used.  But the difference between delete and  
> clear is -- delete ensures the reference you delete will cause an  
> immediate error on use, but does nothing to prevent memory corruption to  
> all the other references to the same memory.  Clear does the same for the  
> reference you clear, but also prevents memory corruption for all the other  
> references to the same memory.  So even though you are in undefined  
> territory, the runtime makes a best effort to avoid you cutting off your  
> head.  The error may still be silent, but it's not deadly.

If in nonrelease mode clear() sets a zombi-mode bit inside the object, the language can then add asserts that stop the program if a zombi object is used (field accessors too need such assert, it's an object invariant).

To reduce the runtime overhead of all those asserts you can do something like C# does with the IDisposable, the language may allow to call clear() only on objects tagged with something like @clearable, so all other objects don't need those asserts.

This is a fully runtime situation and I don't like it a lot. But it's not so different from what C# does.


> It might even be a good idea to zero out the vtable to cause a loud error  
> on the next dynamic cast or virtual function call :)

OK.

Bye,
bearophile