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POUsing conditional statement to select different templated matrix class at run-time
 

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  1. POUsing conditional statement to select different templated matrix class at run-time
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    <p>I'm working with the templated Matrix class in the Eigen linear algebra library (<a href="http://eigen.tuxfamily.org/dox/TutorialMatrixClass.html" rel="nofollow">link</a>). The Matrix class takes three nominal template parameters:</p> <pre><code>Matrix&lt;type, rows, cols&gt; </code></pre> <p>In the above, an example of <code>type</code> is <code>double</code>, or <code>std::complex&lt;double&gt;</code>. In addition, <code>rows</code> is the number of rows, and <code>cols</code> is the number of columns in the Matrix.</p> <p>As shown by the code below, what I would like to do is use a different templated Matrix class at run-time using a conditional statement.</p> <p>The first solution that comes to mind might be to use void pointers.</p> <pre><code>#include &lt;iostream&gt; #include &lt;Eigen/Dense&gt; #include &lt;complex&gt; using namespace Eigen; int main() { // this flag is set at run-time, but it is only set here // in the code as an example int create_complex = 1; void *M; if(create_complex) { Matrix&lt;std::complex&lt;double&gt;,3,3&gt; m0; M = &amp;m0; } else { Matrix&lt;double,3,3&gt; m0; M = &amp;m0; } // de-reference pointer here and use it return 0; } </code></pre> <p>Although this code compiles, the <code>void *M</code> pointer needs to be explicitly de-referenced before use. This is inconvenient, since I then have to write different code blocks for the same program logic.</p> <p>I am wondering if there is something similar to polymorphism that might be applied here, where I don't have to use void pointers.</p>
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    1. USNicholas Kinar
    1. USNicholas Kinar
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    1. COThe `create_complex` flag is not known at compile time. I am simply using `create_complex` as an example.
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      1. USNicholas Kinar
    2. CODo you mind using `boost::variant` ? I'd try very hard to avoid being in your situation (maybe a little more background would help us help you), but if I must, I'd go with it.
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      1. POUsing conditional statement to select different templated matrix class at run-time
      1. USAlexandre C.
    3. CO@AlexandreC.: Sure, I would like to use `boost::variant`. I've used the boost library before, but I can't say that I've heard of that particular container. It seems very interesting. How might I use it?
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      1. USNicholas Kinar
 

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