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POtemplate function specialization problem
 

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    <p>I am using templates to implement a range checked conversion from int to enum. It looks like this:</p> <pre><code>template&lt;typename E&gt; E enum_cast(const int &amp;source); </code></pre> <p>The template function placed more or less in the root-directoy of the project. When defining a new enum that is foreseen to be assigned values from a config file like this:</p> <pre><code>enum ConfigEnum { ConfigEnumOption1 = 'A' , ConfigEnumOption2 = 'B' , ConfigEnumInvalid }; ConfigEnum option = XmlNode.iAttribute("option"); </code></pre> <p>I define a template specialization for this particular enum type in a .cpp-file for the module this enum is used in.</p> <pre><code>template&lt;&gt; ConfigEnum enum_cast(const int &amp;source) { switch(source) { case ConfigEnumOption1 : return ConfigEnumOption1; case ConfigEnumOption2 : return ConfigEnumOption2; default return ConfigEnumInvalid; } </code></pre> <p>Now the assignment of an int to the enum becomes:</p> <pre><code>ConfigEnum option = enum_cast&lt;ConfigEnum&gt;(XmlNode.iAttribute("option")); </code></pre> <p>which makes sure that the enum is allways in valid range. Note that I have not allways control over these enums so this seems to a be reasonable and easily configureable solution. </p> <p>Anyway, this works all very well (although I am not shure all code given here is correct because I just recall it from memory right now)</p> <p>The problem stems from the fact that it might be desireable to use this "enum_cast" construct thorughout the code base whenever an in is assigned to a enum. After all this can be enforced by a simple search-and-replace operation. Of course I do not want to define these specializations for all and every enum around but only for those that need the range check at the moment. I would prefer to add template specializations for the enum types when the need arises and use the assignment operator when no specialization is defined.</p> <p>Thus:</p> <pre><code>InternalEnum internal = enum_cast&lt;InternalEnum&gt;(internal_integer); </code></pre> <p>would effecively call internal = internal_integer. I figure that I need to tell the compiler to use a certain "default" implementation for all enum types that do not have a specialization.</p> <p>My first bet was giving the original template function an implementation like this:</p> <pre><code>template&lt;typename E&gt; E enum_cast(const int &amp;source) { E copy = source; return copy; }; </code></pre> <p>Unfortunately now this is allways called instead of the specialiazations given in the .cpp-files deeper into the project directory-tree.</p> <p>Any thoughts? </p> <p>Thanks in advance Arne</p>
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