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Added section on abstract classes and non-creation of constructor wrappers.

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git-svn-id: https://swig.svn.sourceforge.net/svnroot/swig/trunk/SWIG@4651 626c5289-ae23-0410-ae9c-e8d60b6d4f22
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Dave Beazley 2003-04-02 01:37:45 +00:00
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Doc/Manual/SWIGPlus.html
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@ -237,6 +237,9 @@ void delete_List(List *l) {
}
</pre></blockquote>
<h3>Default constructors</h3>
If a C++ class does not define any public constructors or
destructors, SWIG will automatically create a default constructor or
destructor. However, there are a few rules that define this behavior:
@ -299,8 +302,72 @@ However, this removal may now cause SWIG to erroneously generate constructors
for classes that define a constructor in those sections. Consider restoring
those sections in the interface or using <tt>%nodefault</tt> to fix the problem.
<a name="n8"></a><H3>5.5.2 Copy constructors</H3>
<h3>When constructor wrappers aren't created</h3>
If a class defines a constructor, SWIG normally tries to generate a wrapper for it. However, SWIG will
not generate a constructor wrapper if it thinks that it will result in illegal wrapper code. There are really
two cases where this might show up.
<p>
First, SWIG won't generate wrappers for protected or private constructors. For example:
<blockquote>
<pre>
class Foo {
protected:
Foo(); // Not wrapped.
public:
...
};
</pre>
</blockquote>
<p>Next, SWIG won't generate wrappers for a class if it appears to be abstract--that is, it has undefined
pure virtual methods. Here are some examples:
<blockquote>
<pre>
class Bar {
public:
Bar(); // Not wrappped. Bar is abstract.
virtual void spam(void) = 0;
};
class Grok : public Bar {
public:
Grok(); // Not wrapped. No implementation of abstract spam().
};
</pre>
</blockquote>
Some users are surprised (or confused) to find missing constructor wrappers in their interfaces. In almost
all cases, this is caused when classes are determined to be abstract. To see if this is the case, run SWIG with
all of its warnings turned on:
<blockquote>
<pre>
% swig -Wall -python module.i
</pre>
</blockquote>
In this mode, SWIG will issue a warning for all abstract classes. It is possible to force a class to be
non-abstract using this:
<blockquote>
<pre>
%feature("notabstract") Foo;
class Foo : public Bar {
public:
Foo(); // Generated no matter what---not abstract.
...
};
</pre>
</blockquote>
More information about <tt>%feature</tt> can be found in the <a href="Customization.html">Customization features</a> chapter.
<a name="n8"></a><H3>5.5.2 Copy constructors</H3>
If a class defines more than one constructor, its behavior depends on the capabilities of the
target language. If overloading is supported, the copy constructor is accessible using