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 4<title>PTypes: variant: object references</title>
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10<p><a href="../index.html"><img src="title-21.png" width="253" height="39" alt="C++ Portable Types Library (PTypes) Version 2.1" border="0"></a> 
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13<p class="hpath"><a href="index.html">Top</a>: <a href="basic.html">Basic types</a>: 
14<a href="variant.html">variant</a>: Object references</p>
15<p><br>
16Variants can hold references to objects derived from <span class="lang">component</span>. 
17PTypes performs reference counting, so that assigning variants containing object 
18references can be considered safe: an object will only be destroyed when there 
19are no more references left to it. If you want to control the destruction of an 
20object 'manually', you can increment the reference count with <span class="lang">addref()</span> 
21before assigning a reference to a variant (see <a href="unknown.html">unknown 
22&amp; component</a>). In this case, each call to <span class="lang">addref()</span> 
23should be balanced with a call to <span class="lang">release()</span>.</p>
24<p>It should be noted that the reference counting mechanism has a potential flaw 
25which may lead to memory leaks. Consider two objects containing variants with 
26cross-referencing pointers to each other. The library can not keep track of such 
27circular references, and an attempt to free one of the objects will result in 
28destroying only one of them and leaving the other in the memory without any references 
29to it. This is a known problem and can be solved by either eliminating circular 
30references when designing data structures or by providing a complex memory 'garbage 
31collector' which keeps track of all object references in the program.</p>
32<p class="seealso">See also: <a href="unknown.html">unknown &amp; component</a>, 
33<a href="variant.typecasts.html">Assignments and typecasts</a>, <a href="variant.arrays.html">Arrays</a>, 
34<a href="variant.utils.html">Utilities</a> </p>
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