From: marc.glisse@gmail.com   
      
   Qi  wrote:   
      
   > On 2012-3-15 15:07, Michael wrote:   
   >>   
   >> ... that the compiler doesn't also go ahead and implicitly define   
   >> operator !=() for you?   
   >   
   > Though logically "not ==" is almost same as "!=", the implementation   
   > maybe quite different, especially for performance.   
   >   
   > To implement ==, you need to verify all member fields are equal.   
   > But for !=, you will return when you get first non-equal field.   
      
   Er, no, for both you stop as soon as you find a non-equal field. The   
   only difference is that in one case this early exit returns false and   
   in the other true...   
      
   > Not sure if this is the primary reason the compile doesn't implicit   
   > add !=, but if the compiler add !=, there will be performance issue.   
      
   I have often seen operator== return something that is not bool, but I   
   can't remember ever seing operator!= do something significantly   
   different from !operator==.   
      
      
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