From: daniel.kruegler@googlemail.com   
      
   On 2012-11-16 10:13, Zhihao Yuan wrote:   
   > Non-throw swapable is quite useful, and it can be more useful if the   
   > concept can be tested.  If we already have an object of type T, I   
   > think the following one is enough:   
   >   
   > template    
   > constexpr bool is_nothrow_swapable(T& t) {   
   > 	using std::swap;   
   > 	return noexcept(swap(t, t)) or   
   > 		(std::is_nothrow_move_constructible::value and   
   > 		 std::is_nothrow_move_assignable::value);   
   > }   
   >   
   > However, I want it to be able to work on just a type, to work as an   
   > integral_constant.  Is that doable?  Comments on how to implement an   
   > is_swapable are also welcome.  Thanks.   
      
   I'm not sure whether I understood your question correctly, because you   
   mention (a) the ability to work on just a type and (b) you refer to   
   is_swapable (instead of is_nothrow_swapable). I guess that (b) is just a   
   thinko on your side. What about a variation of your constexpr function   
   so that it does not depend on any argument anymore:   
      
   template    
   constexpr bool is_nothrow_swappable() {   
       using std::swap;   
       return noexcept(swap(std::declval(), std::declval())) or   
   		(std::is_nothrow_move_constructible::value and   
   		 std::is_nothrow_move_assignable::value);   
   }   
      
   template   
   struct is_nothrow_swappable_trait :   
       std::integral_constant()>   
   {   
   };   
      
   ?   
      
   HTH & Greetings from Bremen,   
      
   Daniel Krügler   
      
      
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