From: dave@boostpro.com   
      
   on Wed Jun 06 2012, kispaljr  wrote:   
      
   > I have a bad feeling about this, since such a construction would mean   
   > that e.g. LastElementOf::type would compile to different types   
   > at different points of the source file (before and after adding a new   
   > element), and it seems bogus to me. (It smells like a 'compile time   
   > variable'.) Nevertheless that is exactly what I want now.   
   >   
   > Do you think it is possible somehow? C++11 is allowed.   
   > (I've already asked this on Stack Overflow, but didn't get an answer.)   
      
   You can't do that.  Compile-time C++ is a pure functional language.   
   However, you can still compute anything you want.  You just have to do   
   it by creating new values rather than modifying a value.  That is, you   
   can't "add an element to a list."  Instead, you can "create a new list   
   that contains everything in the old list plus the new element."   
      
        template  struct cons;   
        struct nil;   
      
        typedef cons > some_list;   
      
        // doesn't change some_list   
        typedef cons a_longer_list;   
      
   that's why, in MPL, push_back "returns" a new sequence.   
      
        typedef   
          mpl::push_back::type   
        a_longer_sequence;   
      
   HTH,   
      
   --   
   Dave Abrahams   
   BoostPro Computing   
   http://www.boostpro.com   
      
      
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