[boost] regex_grep: functor copying

From: Darren Cook (darren_at_[hidden])
Date: 2004-01-03 21:36:53

In this code:
   std::string str("...");
   boost::regex re("...");
   MyFunctor callback(this);
   int matches=boost::regex_grep(callback,str,re);
   if(matches==0)return 0;
   if(callback.has_errors)return 2;
   return 1;

it always returns 1 when it should return 2, and this is because the functor 
is being copied rather than passed by reference.

Is there a reason it is copied? Is passing functors by reference a Bad 
Thing, and if so could someone point me to an article or discussion summary 
on this?

In the above case I'm passing in a "this" pointer, so I'll just move 
"has_errors" from the functor into the client class. But this is nearly as 
ugly as using a global variable: the variable will only ever be set by the 
functor, and only ever read by this block of code.

Darren