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POC++ smart pointers: sharing pointers vs. sharing data
 

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    <p>In this <a href="https://web.archive.org/web/20100318031119/http://labs.trolltech.com:80/blogs/2009/08/25/count-with-me-how-many-smart-pointer-classes-does-qt-have" rel="nofollow noreferrer">insightful article</a>, one of the Qt programmers tries to explain the different kinds of smart pointers Qt implements. In the beginning, he makes a distinction between sharing data and sharing the pointers themselves:</p> <blockquote> <p>First, let’s get one thing straight: there’s a difference between sharing pointers and sharing data. When you share pointers, the value of the pointer and its lifetime is protected by the smart pointer class. In other words, the pointer is the invariant. However, the object that the pointer is pointing to is completely outside its control. We don’t know if the object is copiable or not, if it’s assignable or not.</p> <p>Now, sharing of data involves the smart pointer class knowing something about the data being shared. In fact, the whole point is that the data is being shared and we don’t care how. The fact that pointers are being used to share the data is irrelevant at this point. For example, you don’t really care how Qt tool classes are implicitly shared, do you? What matters to you is that they are shared (thus reducing memory consumption) and that they work as if they weren’t.</p> </blockquote> <p>Frankly, I just don't undersand this explanation. There was a clarification plea in the article comments, but I didn't find the author's explanation sufficient.</p> <p>If you <em>do</em> understand this, please explain. What is this distinction, and how are other shared pointer classes (i.e. from boost or the new C++ standards) fit into this taxonomy?</p> <p>Thanks in advance</p>
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    1. USEli Bendersky
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      1. USJohannes Schaub - litb
 

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