5b35552d   
   From: dave@boostpro.com   
      
   on Tue Nov 22 2011, Andrzej Krzemieński  wrote:   
      
   > Hi,   
   > I am trying to implement a template "wrapper" for any arbitrary type,   
   > much like boost::optional. In fact I am trying to write my own   
   > alternative implementation of optional. I want it to have the   
   > following property: if the wrapped type T ptovides copy constructor,   
   > optional also provides a copy constructor; similarly, optional   
   > provides a move constructor iff T provides one. With concepts (as   
   > defined in N2914), I would express it like this:   
   >   
   >   template< typename T >   
   >   struct Optional   
   >   {   
   > 	  requires CopyConstructible   
   > 	  Optional( Optional const& );   
   >   
   >       requires MoveConstructible   
   > 	  Optional( Optional && );   
   >   };   
   >   
   > Do you know of any way to implement similar behavior in C++11? The   
   > enable_if trick does not seem to work for disabling the default   
   > constructor.   
      
   I think you might need to dispatch to different specializations of the   
   whole class template based on the properties of T.   
      
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   Dave Abrahams   
   BoostPro Computing   
   http://www.boostpro.com   
      
      
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