From: jklowden@speakeasy.net   
      
   On Thu,  8 May 2014 06:47:53 CST   
   MARH  wrote:   
      
   > Perhaps I haven't made myself clear, I have a whole set of apples,   
   > with ids; for example:   
   >   
   > AppleID a(7), b(99), c(33);   
   >   
   > And likewise pears with their own ids:   
   >   
   > PearID p(7), q(8), r(1000000)   
   >   
   > and I don't want to be able to compile:   
   >   
   > a = p;   // Bad!   
   > a = b;   // Good.   
      
   If the values (7, 99, 33, etc.) are known at compile time, then enum is   
   your friend.  You haven't said so, but I take it the values are not   
   known, that some external source presents you with integers   
   representing apples and pears, and you'd like to classify them and use   
   C++ to keep them distinct.   
      
   In that case a simple class suffices.  The simplest class (I say   
   boldly) is a struct:   
      
   struct AppleID { int id; AppleID( int id=0 ) : id(id) {} };   
   struct PearID { int id; PearID( int id=0 ) : id(id) {} };   
      
   thus   
      
   > AppleID a(7), b(99), c(33);   
   > PearID p(7), q(8), r(1000000)   
   > a = p;   // Bad!   
   > a = b;   // Good.   
      
   all work, assuming you want a.id == 99 post-assignment.   
      
   In both cases (enum and struct) you're creating a user-defined type,   
   and determining its arithmetic and interchangeablilty properties.   
      
   HTH.   
      
   --jkl   
      
      
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