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    <p>I'm not entirely sure what you are asking about. I thought the sample you gave was interesting and played a little bit with it.</p> <p>I came up with an implementation that makes <code>span&lt;a,b&gt;</code> to be a <em>template alias</em> for <code>indexes&lt;a, ..., b&gt;</code>, using the trick of type deduction in <code>constexpr</code> functions:</p> <pre><code>template &lt;int a, int b&gt; using span = decltype(expand_span&lt;a,b&gt;()); </code></pre> <p>Now you can have your cake and eat it:</p> <pre><code>//////////////////////////////////////////////////////////////// // using indirect template arguments template&lt;typename&gt; struct indirect_work { }; void test_indirect() { indirect_work&lt;indexes&lt;1,2,3,4&gt;&gt; x; indirect_work&lt;span&lt;1,4&gt;&gt; y; x = y; // x and y are of identical types static_assert(std::is_same&lt;indexes&lt;1,2,3,4&gt;, span&lt;1,4&gt;&gt;::value, "fact check"); } </code></pre> <p>But, perhaps more interestingly, <strong>you can still have your primary <code>work</code> template take a raw <code>&lt;int...&gt;</code></strong> template argument list: </p> <pre><code>//////////////////////////////////////////////////////////////// // using direct template arguments template&lt;int...&gt; struct direct_work { }; // deduction alias: template&lt;int... direct&gt; constexpr direct_work&lt;direct...&gt; deduction_helper(indexes&lt;direct...&gt;); template &lt;typename Idx&gt; using deduce = decltype(deduction_helper(Idx{})); void test_direct() { direct_work&lt;1,2,3,4&gt; x; deduce&lt;indexes&lt;1,2,3,4&gt;&gt; y; deduce&lt;span&lt;1,4&gt;&gt; z; static_assert(std::is_same&lt;decltype(x), decltype(y)&gt;::value, "fact check"); static_assert(std::is_same&lt;decltype(x), decltype(z)&gt;::value, "fact check"); } </code></pre> <p>See a complete working demonstration here: <a href="http://ideone.com/U2geNF" rel="noreferrer">gcc on ideone</a>. I compiled it with clang locally.</p> <hr> <h3>Full code</h3> <p>Code for <code>expand_span</code> duplicated here in case link should go dead:</p> <pre><code>#include &lt;type_traits&gt; template &lt;int...&gt; struct indexes {}; namespace { template&lt;int a, int... other&gt; constexpr indexes&lt;a, other...&gt; combine(indexes&lt;other...&gt; deduce); template&lt;int a, int b, typename Enable = void&gt; struct expand_span_; // primary template&lt;int a, int b&gt; struct expand_span_&lt;a, b, typename std::enable_if&lt; (a==b), void &gt;::type&gt; { static constexpr indexes&lt;a&gt; dispatch(); }; template&lt;int a, int b&gt; struct expand_span_&lt;a, b, typename std::enable_if&lt; (a&lt;b), void &gt;::type&gt; { static constexpr decltype(combine&lt;a&gt;(expand_span_&lt;a+1, b&gt;::dispatch())) dispatch(); }; template&lt;int a, int b&gt; constexpr auto expand_span() -&gt; decltype(expand_span_&lt;a,b&gt;::dispatch()); } template &lt;int a, int b&gt; using span = decltype(expand_span&lt;a,b&gt;()); //////////////////////////////////////////////////////////////// // using indirect template arguments template&lt;typename&gt; struct indirect_work { }; void test_indirect() { indirect_work&lt;indexes&lt;1,2,3,4&gt;&gt; x; indirect_work&lt;span&lt;1,4&gt;&gt; y; x = y; // x and y are of identical types static_assert(std::is_same&lt;indexes&lt;1,2,3,4&gt;, span&lt;1,4&gt;&gt;::value, "fact check"); } //////////////////////////////////////////////////////////////// // using direct template arguments template&lt;int...&gt; struct direct_work { }; // deduction alias: template&lt;int... direct&gt; constexpr direct_work&lt;direct...&gt; deduction_helper(indexes&lt;direct...&gt;); template &lt;typename Idx&gt; using deduce = decltype(deduction_helper(Idx{})); void test_direct() { direct_work&lt;1,2,3,4&gt; x; deduce&lt;indexes&lt;1,2,3,4&gt;&gt; y; deduce&lt;span&lt;1,4&gt;&gt; z; static_assert(std::is_same&lt;decltype(x), decltype(y)&gt;::value, "fact check"); static_assert(std::is_same&lt;decltype(x), decltype(z)&gt;::value, "fact check"); } int main() { test_indirect(); test_direct(); } </code></pre>
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    1. POWhat are the expression syntax over types C++ support?
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    1. COThanks, but I am not looking for how to implement that `work` class. If you look at the question, I am asking what all I can put inside `<>` as template type argument. We have fairly clear idea about EDSL, but how much expressive things can we write as type argument?
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    2. COPS. have you looked at ProtoV5 (https://github.com/ericniebler/proto-0x)? It uses function types extensively to mimic EDSLs in it's template arguments. E.g. [A First Look at Proto-0x](http://www.youtube.com/watch?v=JF6YM0XzHnE), e.g. `constexpr map_list_of_expr<terminal(map_list_of_)> map_list_of {};` on [slide 37](https://github.com/boostcon/cppnow_presentations_2013)
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    3. COYes, I had noticed proto has those beautiful function types, the other intuitive syntax's are T[N] to say N times T (who uses raw array anymore!) , and T* to say zero or more T (again who uses native pointer?) . I do not know if c++14 object alias/expression alias will give something more beautiful like `tuple<3_times<T> >`
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