Thread: auto_ptr in exception safety design

Hello everyone,


What I am confused is about,

http://www.gotw.ca/gotw/059.htm

--------------------
Indeed, often the best way to implement the Pimpl idiom is exactly as shown in Example 4 above, by using a pointer (in order to take advantage of nonthrowing operations) while still wrapping the dynamic resource safely in an auto_ptr manager object. Just remember that now your object must provide its own copy construction and assignment with the right semantics for the auto_ptr member, or disable them if copy construction and assignment don't make sense for the class.
--------------------

1. What means "the right semantics for the auto_ptr member"?

2. "disable" means for the class, copy construction and assignment are not needed? Curious. Never thought of a class which does not need that two basic functions. :-)


thanks in advance,
George

Thanks CornedBee,


I understand what is deep copy. But I am not quite sure about what do you mean "clone the implementation".

Do you mean copy the object pointed by auto_ptr, other than copy the auto_ptr member itself?

Originally Posted by CornedBee

1) Means it must clone the implementation to perform a deep-copy.

regards,
George

> But I am not quite sure about what do you mean "clone the implementation".

The only thing auto-ptr really does is delete the object it holds when it falls out of scope. It acts like a bald pointer in every other respect, so when you need separate pointers (like you would here) you have to do a deep copy. So think about the implementation for a deep copy with a bald pointer, and the phrase should make some sense.

Hi citizen,


"bald pointer" you mean raw pointer?

Originally Posted by citizen

> But I am not quite sure about what do you mean "clone the implementation".

The only thing auto-ptr really does is delete the object it holds when it falls out of scope. It acts like a bald pointer in every other respect, so when you need separate pointers (like you would here) you have to do a deep copy. So think about the implementation for a deep copy with a bald pointer, and the phrase should make some sense.

regards,
George

Sure, same difference.

Thanks citizen and iMalc,


Question answered.

Originally Posted by iMalc

I/O Streams are a classic example of something that should not be copyable. Singletons are another.

regards,
George