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    <p>N.B. this part of your question is not possible:</p> <pre><code>template&lt;class Packed&gt; struct foo : unpack&lt;Packed&gt;::type...{}; </code></pre> <p><code>Packed</code> is not a parameter pack here, so cannot be used in a pack expansion. If you changed it to:</p> <pre><code>template&lt;class Packed&gt; struct foo&lt;packed&lt;Packed...&gt; : unpack&lt;Packed&gt;::type...{}; </code></pre> <p>then you could expand the parameter pack, but now <code>unpack</code> would only be passed a single type, and would have no way to know which index it was, i.e. what <code>N</code> should be for <code>node&lt;Pn, N&gt;</code></p> <p>To make it work you need to combine the type parameter pack with a non-type parameter pack of integers, which your <code>values</code> gets close to, but you have the indirection of deriving from <code>unpack</code> not a list of <code>node</code> types.</p> <p>I think this is what you're asking for (edited after misunderstanding the <code>node</code> part), using my <a href="https://gitorious.org/redistd/redistd/blobs/master/include/redi/index_tuple.h" rel="nofollow noreferrer"><code>index_tuple</code></a> utility, which could easily be replaced by litb's <a href="https://stackoverflow.com/a/7858971/981959"><code>seq</code></a> template or any similar type. The non-type parameter pack of integers is deduced as a default template argument and can then be used in the base-class list of <code>foo</code>:</p> <pre><code>#include &lt;redi/index_tuple.h&gt; template&lt;typename T, unsigned N&gt; struct node { }; template&lt;typename... T&gt; struct packed { }; template&lt;typename T&gt; struct index_tuple_from_packed; template&lt;typename... T&gt; struct index_tuple_from_packed&lt;packed&lt;T...&gt;&gt; { typedef redi::to_index_tuple&lt;T...&gt; type; }; template&lt;typename T, typename I = typename index_tuple_from_packed&lt;T&gt;::type&gt; struct foo; template&lt;typename... T, unsigned... Indices&gt; struct foo&lt;packed&lt;T...&gt;, redi::index_tuple&lt;Indices...&gt;&gt; : node&lt;T, Indices&gt;... { }; struct A { }; struct B { }; struct C { }; int main() { typedef packed&lt;A, B, C&gt; p; foo&lt;p&gt; d; node&lt;A, 0&gt;* a = &amp;d; node&lt;B, 1&gt;* b = &amp;d; node&lt;C, 2&gt;* c = &amp;d; } </code></pre>
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    1. POcan a type tuple be unpacked later?
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    1. USCommunity
    1. USJonathan Wakely
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    1. COI guess "index_tuple" or "seq" are nearly same as "values" and value_gen in my example. See later part of the example. You are using make_derived<...>::type as the implementation, while I am looking for make_derived to look like that (in my example it is foo).though I can use template alias for that but I want to have a class template instead of alias.
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    2. COI got rid of `make_derived`, please reload
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    3. COThis is very close to the solution, however as foo is to take variadic types, it is not possible to add default type at end. I agree some confusion about foo is in the question. Look at the last part, where template<class...>foo; is defined.
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