From: musiphil@bawi.org   
      
   On 2011-12-06 12:00, Nevin ":-]" Liber wrote:   
   >   
   > The compromise I use for these situations is to define operator< but not   
   > > , <= or >=.   
   >   
   > The problem is composibility.  If you go down the path of std::less   
   > instead of operator<, and you want to use that type as a member of   
   > another class that you wish to be able to use as a key in a set or a   
   > map, you have to define a std::less for your new class (after all, if   
   > the actual ordering for your original type is meaningless, any ordering   
   > based on it is also meaningless).  It gets very clunky very quickly.   
      
   Even if you use define operator< for T, which is a member of class S,   
   op< for S doesn't automatically get composed out of op< for T, but you   
   have to manually write op< for S using op< for T, just as with   
      
       struct complex { int re, im; };   
      
   op< for complex doesn't automatically get composed but you have to write   
      
       bool operator<(complex a, complex b) { /* ... */ }   
      
   So the difference between defining operator< and defining std::less   
   is negligible in this regard. Either way, you have to write a composite   
   comparator function using the comparator functions of its members.   
      
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