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POAutomatically separate class definitions from declarations?
 

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  1. POAutomatically separate class definitions from declarations?
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    <p>I am using a library that consists almost entirely of <strong>templated classes and functions in header files</strong>, like this:</p> <pre><code>// foo.h template&lt;class T&gt; class Foo { Foo(){} void computeXYZ() { /* heavy code */ } }; template&lt;class T&gt; void processFoo(const Foo&lt;T&gt;&amp; foo) { /* more heavy code */ } </code></pre> <p>Now this is bad because <strong>compile times are unbearable</strong> whenever I include one of those header files (and actually I include many of them in each of my compilation units).</p> <p>Since as a template parameter I only use one or two types anyway I am planning to create, for each library header file, <strong>a file that contains only declarations</strong>, without the heavy code, like this:</p> <pre><code>// NEW: fwd-foo.h template&lt;class T&gt; class Foo { Foo(); void computeXYZ(); }; template&lt;class T&gt; void processFoo(const Foo&lt;T&gt;&amp; foo); </code></pre> <p>And then one file that creates all the instantiations that I'll need. That file can be <strong>compiled separately once and for all</strong>:</p> <pre><code>// NEW: foo.cpp #include "foo.h" template class Foo&lt;int&gt;; template class Foo&lt;double&gt;; template void processFoo(const Foo&lt;int&gt;&amp; foo); template void processFoo(const Foo&lt;double&gt;&amp; foo); </code></pre> <p>Now I can just include <code>fwd-foo.h</code> in my code and have short compile times. I'll link against <code>foo.o</code> at the end. </p> <p>The downside, of course, is that I have to create these new <code>fwd-foo.h</code> and <code>foo.cpp</code> files myself. And of course it's a maintenance problem: When a new library version is released I have to adapt them to that new version. Are there any other downsides?</p> <p>And my main question is: </p> <p>Is there any chance I can create these new files, especially <code>fwd-foo.h</code>, <strong>automatically</strong> from the original <code>foo.h</code>? I have to do this for many library header files (maybe 20 or so), and an automatic solution would be best especially in case a new library version is released and I have to do this again with the new version. Are any tools available for this task?</p> <p><strong>EDIT:</strong> </p> <p>Additional question: How can the newly supported <code>extern</code> keyword help me in this case?</p>
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