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copied!<p>The only purpose of <code>foo</code> in the OP is triggering the check when it's instantiated. That's why you need the variable <code>hello</code>: it's an instantiation of <code>foo</code>.</p> <p>I would rather follow the approach of traits in <code><type_traits></code>. More precisely, I would turn <code>perform_checks</code> into <code>class</code> (or <code>struct</code>) that has public <code>static constexpt bool</code> member called <code>value</code> which is <code>true</code> or <code>false</code> depending on whether the given types pass the test or not. Then I would use a single <code>static_assert</code> to stop compilation if <code>value</code> is false.</p> <p>My solution, which assumes that the number of template type arguments is even, follows:</p> <pre><code>#include <type_traits> template<typename First, typename Second, typename... Others> struct perform_checks : std::integral_constant<bool, perform_checks<First, Second>::value && // Checks First and Second perform_checks<Others...>::value // Recursively "calls" itself on Others > { }; // This specialization finishes the recursion and effectively performs the test template<typename First, typename Second> struct perform_checks<First, Second> : std::integral_constant<bool, std::is_default_constructible<First>::value && // Checks First std::is_copy_constructible<Second>::value // Checks Second > { }; </code></pre> <p>Here is a simple test:</p> <pre><code>struct NonDefaultConstructible { NonDefaultConstructible() = delete; }; struct NonCopyConstructible { NonCopyConstructible(const NonCopyConstructible&) = delete; }; int main() { static_assert(perform_checks<int, double>::value, "Failure"); static_assert(perform_checks<int, int, double, double>::value, "Failure"); static_assert(!perform_checks<NonDefaultConstructible, int>::value, "Failure"); static_assert(!perform_checks<int, NonCopyConstructible>::value, "Failure"); static_assert(!perform_checks<int, int, double, NonCopyConstructible>::value, "Failure"); } </code></pre> <p>Notice that no variable was created.</p>

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