From: PChapin@vtc.vsc.edu   
      
   On 2014-05-08 08:46, Gonzalo BG wrote:   
      
   > But in summary, C++ is a very bad language for this _right now_. Since   
   > you cannot write an user-defined integer class models an Integral   
   > concept and use it with the rest of the language and standard library.   
   >   
   > In Haskell this all works flawlessly since: newtype allows you to easily   
   > create new types from existing ones, and typeclasses (concepts) are used   
   > everywhere.   
      
   At the risk of being off topic I might also mention that Ada supports   
   this ability very well. What the OP is trying to do is trivial:   
      
   type Apple_ID is new Integer;   
   type Pear_ID is new Integer;   
      
   Now objects of type Apple_ID and Pear_ID can't be mixed (or mixed with   
   integers) yet they inherit all the values and operations of Integer.   
   However it is true that to support this there are pervasive effects on   
   the language. For example indexing an array by an Apple_ID is a type   
   error unless you define an array type specifically that can accept such   
   an index   
      
   type Flavor_Array_Type is array(Apple_ID range 1 .. 10) of Flavor;   
      
   An object of type Flavor_Array_Type can only be indexed by Apple_ID (and   
   not integers), etc.   
      
   The Ada community regards this as a strong feature because it allows you   
   to create scalar types for logically distinct concepts and let the type   
   system catch errors involving them... such as mixing an apple counter   
   value with a buffer offset, etc.   
      
   I've often thought that creative use of C++ templates could probably   
   realize many of the same goals but it would be a rather heavy handed way   
   of emulating what, at its heart, is a simple concept. Also, as was   
   pointed out, since the C++ language and library does not "think" this   
   way, I expect aggressive use of distinct scalar types would be an uphill   
   battle in typical C++ code bases.   
      
      
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