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   On Tuesday, March 11, 2014 3:20:01 PM UTC+8, Daniel Krügler wrote:   
   > In C++11 the effects of the move/copy-assignment operators depends on   
   >   
   > the nature of the allocators in source and target. This is specified in   
   >   
   > [container.requirements.general] p8:   
   >   
   >   
   >   
   > "[..] The allocator may be replaced only via assignment or swap().   
   >   
   > Allocator replacement is performed by copy assignment, move assignment,   
   >   
   > or swapping of the allocator only if   
   >   
   >   
   allocator_traits::propagate_on_container_copy_assignment::va   
   lue,   
   >   
   >   
   allocator_traits::propagate_on_container_move_assignment::va   
   lue,   
   >   
   > or allocator_traits::propagate_on_container_swap::value   
   >   
   > is true within the implementation of the corresponding container   
   >   
   > operation. [..]"   
   >   
   >   
   >   
   > The implication of this wording is that if allocator replacement happens   
   >   
   > during copy/move assignment, then the previous storage must be freed   
   >   
   > (and thus the capacity reduced to zero during the operation which   
   >   
   > corresponds to an effective reduction of the capacity). It is IMO not   
   >   
   > really clear from the wording, whether in such a situation an   
   >   
   > implementation is required or allowed to check for allocator equality   
   >   
   > when propagate_on_container_copy/move_assignment return true and to   
   >   
   > finally decide on reallocation depending on the outcome of that test.   
   >   
   >   
      
   Hi Daniel,   
      
   Thank you very much for replying with detailed information.  I think   
   I'm now clear regarding vector::clear() and   
   vector::operator=(initializer_list).   
      
   For copy/move assignment, I now understand that when allocator   
   replacement happens, reallocation and reduction of capacity may well   
   happen.  But what if   
   allocator_traits::propagate_on_container_copy_assignment()/a   
   llocator_traits::propagate_on_container_move_assignment()   
   is false (and in the case of move assignment, the target and source   
   allocator does not compare equal), can we be assured that reduction of   
   capacity won't take place?   
      
   Thanks,   
   Goodbyeera   
      
      
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