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Extern template tweaks

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Document extern template functions support.
Extern templates result in new warning to differentiate
from template explicit instantiation definition warning.
This commit is contained in:
William S Fulton 2022-01-25 00:28:08 +00:00
commit 017900d57e
8 changed files with 89 additions and 16 deletions
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Doc/Manual/CPlusPlus11.html
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@ -144,14 +144,39 @@ When either of these is used from a target language, a runtime call is made to o
<H3><a name="CPlusPlus11_extern_template">7.2.3 Extern template</a></H3>
<p>SWIG correctly parses the keywords <tt>extern template</tt>.
<p>SWIG correctly parses <tt>extern template</tt> explicit instantiation declarations.
However, this template instantiation suppression in a translation unit has no relevance outside of the C++ compiler and so is not used by SWIG.
SWIG only uses <tt>%template</tt> for instantiating and wrapping templates.</p>
SWIG only uses <tt>%template</tt> for instantiating and wrapping templates.
Consider the class template below:
</p>
<div class="code"><pre>
template class std::vector&lt;int&gt;; // C++03 explicit instantiation in C++
extern template class std::vector&lt;int&gt;; // C++11 explicit instantiation suppression in C++
%template(VectorInt) std::vector&lt;int&gt;; // SWIG instantiation
// Class template
template class std::vector&lt;int&gt;; // C++03 template explicit instantiation definition in C++
extern template class std::vector&lt;int&gt;; // C++11 template explicit instantiation declaration (extern template)
%template(VectorInt) std::vector&lt;int&gt;; // SWIG template instantiation
</pre></div>
<p>
The above result in warnings:
</p>
<div class="shell">
<pre>
example.i:2: Warning 320: Explicit template instantiation ignored.
example.i:3: Warning 327: Extern template ignored.
</pre>
</div>
<p>
Similarly for the function template below:
</p>
<div class="code"><pre>
// Function template
template void Func&lt;int&gt;(); // C++03 template explicit instantiation definition in C++
extern template void Func&lt;int&gt;(); // C++11 template explicit instantiation declaration (extern template)
%template(FuncInt) Func&lt;int&gt;; // SWIG template instantiation
</pre></div>
<H3><a name="CPlusPlus11_initializer_lists">7.2.4 Initializer lists</a></H3>