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copied!<p>If it is possible for your use-case, you could do specialization on a namespace basis and then aggregate as follows, using C++11 since you mentioned it but can work without.</p> <p>Assume you have a number of namespaces <code>ns_1</code> to <code>ns_k</code> like this:</p> <pre><code>namespace ns_i { template<class T> struct my_int: std::integral_constant<int, -1> {}; /*...*/ enum e_1 { /*...*/ }; template<> struct my_int<e_1>: std::integral_constant<int, 101> {}; /*...*/ enum e_n { /*...*/ }; template<> struct my_int<e_n>: std::integral_constant<int, 142> {}; /*...*/ } </code></pre> <p>I assume you already have the means to do a unique numbering. Then you aggregate the <code>my_int</code> from all namespaces like this:</p> <pre><code>namespace your_lib { template< class T, template<class> class sources... /* any number of template classes, each taking one type argument */ > struct Union: std::integral_constant<int, -1> {}; // default -1 for (empty template list) template< class T, template<class> class source, // match first template template<class> class sources... // match all but first template > struct Union<T, source, sources...>: std::conditional< source::value == -1, union<T, sources...>, // recursively call union on all but first tempalte source // or if there's a value in first, use it > {}; template<class T> struct my_int : Union<T, ns_1::my_int, /*...,*/ ns_k::my_int> {}; /* here you could use boost preprocessor to iterate over the namespaces since you mentionned it */ } </code></pre>

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