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POCombining templates and inheritance in tree conversion
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  1. POCombining templates and inheritance in tree conversion
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    copied!<p>I have data stored in a C++ tree structure which I read in from a file. The tree looks like that:</p> <pre><code>class BaseNode { std::vector&lt;BaseNode*&gt; children_; ... }; class WhiteNode : public BaseNode { ... }; class BlackNode : public BaseNode { ... }; </code></pre> <p>After the tree is built, I would like to convert it, e.g. to a string.</p> <p>In order to keep the tree code separate from the conversion code, I would like to use templates, i.e. implementing something like that:</p> <pre><code>template &lt;class T&gt; T WhiteNode::Convert() { ... }; </code></pre> <p>However, since the tree nodes are stored as <code>BaseNode*</code>, I don't know how to access such a template member function. And since template member functions cannot be inherited, I don't think this will work.</p> <p>I did come up with a working solution, though:</p> <pre><code>class BaseConversion { public: virtual ~BaseConversion() {} virtual void * FromBlack() = 0; virtual void * FromWhite() = 0; }; template &lt;class T&gt; class Conversion : public BaseConversion { public: void * FromBlack(); void * FromWhite(); }; class BaseNode { std::vector&lt;BaseNode*&gt; children_; virtual void * Convert(BaseConversion * conversion) = 0; public: virtual ~BaseNode() {} template &lt;class T&gt; T Convert() { return *static_cast&lt;T*&gt;(Convert(new Conversion&lt;T&gt;)); } }; class WhiteNode : public BaseNode { void * Convert(BaseConversion * conversion) { return conversion-&gt;FromWhite(); } }; class BlackNode : public BaseNode { void * Convert(BaseConversion * conversion) { return conversion-&gt;FromBlack(); } }; </code></pre> <p>And the transformation logic can be entirely separate:</p> <pre><code>template &lt;&gt; void * Conversion&lt;std::string&gt;::FromWhite() { return new std::string("converting WHITE node to std::string ..."); } template &lt;&gt; void * Conversion&lt;std::string&gt;::FromBlack() { return new std::string("converting BLACK node to std::string ..."); } </code></pre> <p>Testing the code:</p> <pre><code>BaseNode * node = new BlackNode; std::cout &lt;&lt; node-&gt;Convert&lt;std::string&gt;() &lt;&lt; std::endl; node = new WhiteNode; std::cout &lt;&lt; node-&gt;Convert&lt;std::string&gt;() &lt;&lt; std::endl; </code></pre> <p>returns the expected result:</p> <pre><code>converting BLACK node to std::string ... converting WHITE node to std::string ... </code></pre> <p>Although this solution works, I am sure it can be done much easier. Any other, simpler solution I came up with failed, e.g. due to type erasure.</p> <p>I would appreciate any help on that. Thanks!</p>
 

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