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Add Python struct member limitation documentation

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Closes #1336
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William S Fulton 2018-11-06 17:13:50 +00:00
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Doc/Manual/Python.html
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@ -1480,6 +1480,27 @@ everything works just like you would expect. For example:
</pre>
</div>
<p>
Note that there is a limitation with structs within structs that will cause a problem
if the outer struct is not a named variable in Python. The following will cause a segfault:
</p>
<div class="targetlang">
<pre>
Bar().f.a = 3
</pre>
</div>
<p>
because the unnamed Python proxy class for <tt>Bar()</tt> has its reference count
decremented by the Python interpreter after <tt>f</tt> has been obtained from it and
before <tt>f</tt> is used to obtain <tt>a</tt>.
This results in the underlying <tt>Bar</tt> instance being deleted, which of course also deletes
<tt>f</tt> inside it. Hence the pointer to <tt>f</tt> points to deleted
memory and use of it results in a segfault or some sort of other undefined behaviour.
</p>
<H3><a name="Python_nn20">38.3.7 C++ classes</a></H3>