From: daniel.kruegler@googlemail.com   
      
   Am 22.11.2012 20:28, schrieb Zhihao Yuan:   
   > On Thursday, 22/11/2012 1:46:09 AM UTC-6, Frank Birbacher wrote:   
   >> Does to following code reliably construct a pair that holds a given   
   >> value twice? Is it true that pair::first will be constructed before   
   >> pair::second? Does make_pair only forward arguments?   
   >   
   > No.  Actually, It copies its argument first, then copies t and move t   
   > into make_pair's argument list, in an indeterminate sequence.  The   
   > moving /b/ can happen before the copying /a/.   
      
   No, it is not moving nor copying the arguments at that point - std::move   
   really is a red herring. The call to std::move just produces an xvalue   
   of T (assuming that T is not an lvalue-reference). Certainly the   
   arguments are evaluated in an indeterminate sequence, but I don't see   
   how that matters in this case. The actual copy/move operation happens in   
   the /mem-initializer-list/ which again is evaluated in order, thus the   
   actual move-construction of second will happen after the   
   copy-construction of first.   
      
   (I'm ignoring std::reference_wrapper-unpacking, but in this case there   
   is no "move" of a value taking place)   
      
   HTH & Greetings from Bremen,   
      
   Daniel Krügler   
      
      
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