From: bouncer@dev.null   
      
   Zoltan Juhasz wrote:   
      
   > On Monday, 21 May 2012 15:28:09 UTC-4, Gene Bushuyev  wrote:   
   >> To avoid default constructing an object one would need the function   
   >> returning by value, how about simply modifying pop to return a value:   
   >>   
   >> template   
   >> T priority_queue::pop()   
   >> {   
   >>     T tmp(move(container.front()));   
   >>     container.erase(container.begin());   
   >>     make_heap(container.begin(), container.end(), compare);   
   >>     return tmp;   
   >> }   
   >>   
   >> It will not break existing code that relies on copy and assumes pop()   
   >> doesn't return anything.   
   >   
   > Unfortunately this implementation does not provide strong exception   
   > safety guarantees, e.g. if an exception is thrown when you return tmp,   
   > the container has been already modified, in an irreversible way, and   
   > the returned element is lost.   
      
   Which is why, as Seungbeom Kim suggested, this version of pop() should   
   only be enabled if T has a non-throwing move constructor (or, if   
   it doesn't have a move constructor, a non-throwing copy constructor).   
      
   - Wil   
      
      
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