TDPL: Manual invocation of destructor

[Steven Schveighoffer]

On Mon, 09 Aug 2010 08:28:38 -0400, Andrej Mitrovic  
<andrej.mitrovich at gmail.com> wrote:

> It's rather perplexing, isn't it? It states in TDPL:
>
> "After you invoke clear, the object is still alive and well, but its
> destructor has been called and the object is now carrying its
> default-constructed stated. During the next garbage collection, the
> destructor is called again, because the garbage collector has no idea in
> what state you have left the object."

This seems totally wrong, what if an object has no default constructor?   
The spec used to say (maybe it still does) that a destructor is guaranteed  
to only ever be called once.

I honestly thought the point of clear was to simply leave the memory in  
place as a kind of "zombie" object until the GC could collect it, to avoid  
having the block get recycled into a new object, and then use an old  
reference to it (via delete).  I didn't know someone would ever  
purposefully use it.  What is the point of calling clear then, if clear  
doesn't get rid of the object and leave it uninitialized?

> But in what situation would you want to manipulate an object that was
> already cleared and ready for garbage collection?

None.  That's the point.  clear is saying "I don't want to use this object  
any more".  The runtime (I thought) was just being conservative and  
leaving the memory in place until it could verify there were no other  
pointers to it.

I'm starting to climb the fence into the "leave delete in the language"  
camp...

-Steve