From: francis.glassborow@btinternet.com   
      
   On 10/04/2012 22:38, Martin B. wrote:   
   > On 10.04.2012 20:00, Ulrich Eckhardt wrote:   
   >> Am 10.04.2012 11:18, schrieb rossmpublic@gmail.com:   
   >>> I have a very simple question that I have been unable to find a   
   >>> satisfactory answer. The question is why do I need to manually   
   >>> optimize my functions using const references?   
   >>>   
   >>> For example:   
   >>> ...   
   >>   
   >> Even worse:   
   >> ...   
   >>   
   >> The performance of course depends on the actual implementation, but   
   >> in common implementations a reference is just a "self-dereferencing   
   >> pointer", so a reference requires another level of   
   >> indirection. Also, any function can cheat and const_cast, so a   
   >> calling function must not assume that the call doesn't modify the   
   >> passed object. ...   
   >   
   > Interesting point. Who at which level is required to assume that   
   > something passed by const-ref is modified by the callee?   
      
   Which reminds me that C++11 supports concurrency. Pass by value only   
   needs unique access at the call site, pass by const reference requires   
   it throughout the life of the function call.   
      
   Francis   
      
      
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