From: bouncer@dev.null   
      
   Seungbeom Kim wrote:   
      
   > On 2012-05-20 21:19, Zoltan Juhasz wrote:   
   [snip]   
   >> for example:   
   >>   
   >> value_type faulty_pop()   
   >> {   
   >>   auto e = move_if_noexcept( internal_top() );   
   >>   internal_pop();   
   >>   return e;   
   >> }   
   >>   
   >> does not provide strong exception guarantees, b/c when you return   
   >> 'e', an exception might occur, and at that point you've changed the   
   >> container in an irreversible way.   
   >   
   > Can't we enable that function only for value_types with a   
   > non-throwing move constructor?   
   >   
   >> The pop( value_type& e ), on the other hand, does not suffer from   
   >> these kind of problems;   
   >   
   > But then you need to default construct an object of value_type and   
   > ask the top element to be move-assigned to it. It may not be always   
   > possible or desirable to default construct such an object, just to   
   > be overwritten later.   
      
   I agree.  Paradoxically, a movable type without a default constructor   
   seems like a strange beast, because it presumably implements a "valid,   
   but resourceless" state for its objects to be left in after having   
   been moved from.   
      
   I would say that a type with a default constructor clearly advertises   
   that such a state exists and must be reckoned with.   
      
   - Wil   
      
      
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