auto_ptr in exception safety design

This is a discussion on auto_ptr in exception safety design within the C++ Programming forums, part of the General Programming Boards category; 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 ...

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    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

  2. #2
    Cat without Hat CornedBee's Avatar
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    1) Means it must clone the implementation to perform a deep-copy.

    2) There's lots of them.
    All the buzzt!
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    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?

    Quote Originally Posted by CornedBee View Post
    1) Means it must clone the implementation to perform a deep-copy.

    regards,
    George

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    Registered User whiteflags's Avatar
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    > 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.

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    Hi citizen,


    "bald pointer" you mean raw pointer?

    Quote Originally Posted by citizen View Post
    > 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

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    Registered User whiteflags's Avatar
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    Sure, same difference.

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    Algorithm Dissector iMalc's Avatar
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    Quote Originally Posted by George2 View Post
    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. :-)
    I/O Streams are a classic example of something that should not be copyable. Singletons are another.
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    Thanks citizen and iMalc,


    Question answered.

    Quote Originally Posted by iMalc View Post
    I/O Streams are a classic example of something that should not be copyable. Singletons are another.

    regards,
    George

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