New shared pointer

[Frerich Raabe]

Moin,

the current shared pointer implementation in KShared/KSharedPtr is a little 
too simplistic IMHO:

- it requires all classes with onto whose objects you want to point with a 
KSharedPtr to provide the interface given by KShared; in practice, this means 
that you might have to change the code of the target class because you either 
need to make it inherit KShared, or you add the ref()/deref() functions

- it provides an implicit conversion to T* which is very evil. For instance, 
this works:

	KSharedPtr<Widget> p( new Foo );
	KSharedPtr<Widget> q = p;
	delete p;
	q->doStuff(); // boom!

This is especially likely to happen when you're porting code to KSharedPtr 
because you might forget to remove a delete call. I noticed that somebody 
added my name to the corresponding entry in kdelibs/TODO which points these 
things out so here's a try at a slightly less simplistic (yet by no means 
comprehensive) shoot at a shared pointer. It's very much like the old 
KSharedPtr, except that

- you don't have to inherit KShared anymore, you can use it with any type.
- it doesn't have an implicit conversion to T* so you cannot accidentally 
delete the internal object. You can still use the get() function to retrieve 
the raw pointer if you really need to.
- the data() function had a weird name - get() is not much better I guess, but 
a few other shared pointer implementations use that name, so I went for it. 
Feel free to suggest something more appropriate.

Note that this new KSharedPtr is not like QSharedDataPointer because it does 
not do copy-on-write (it doesn't automatically detach() when using the 
non-const * and -> operators) - it features a copy() function though, so you 
can have explicitely shared objects.

Please have a look and point stuff out which is worth being pointed out. It's 
still kinda rough (I only tested it with a few code snippets), but you'd get 
the idea what's supposed to happen. I'm very well aware that this is a great 
bikeshed topic but please refrain from endless theoretical discussions. I'd 
appreciate proper C++ code which breaks when using this class or straight 
"Looks okay, we can give it a try and see what breaks", tho.

- Frerich

P.S.: I considered using QSharedData/QSharedDataPointer but that duo has 
exactly the same two problems as KShared/KSharedPtr I mentioned above. I also 
considered boost::shared_ptr but noticed that it pulls in a lot of other 
funky template magic (which, as the honest tears of a certain SUSE engineer 
agree with, might be a little too much for the compiler of choice).
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