Re: [Boost-users] [mpl] insert not inserting?

From: Ovanes Markarian (om_boost_at_[hidden])
Date: 2007-03-28 17:33:46

I think the problem is in the typedef statement below:

typedef mpl::insert<Constraints,
                       mpl::end<Constraints>,
                       Base> BaseClasses;

mpl::insert is an own type but you need the new sequence type with is
accessed via:
mpl::insert<...>::type

Best Regards,
Ovanes
 

-----Original Message-----
From: Scott Meyers [mailto:usenet_at_[hidden]] 
Sent: Donnerstag, 29. März 2007 00:28
To: boost-users_at_[hidden]
Subject: [Boost-users] [mpl] insert not inserting?

In my continuing effort to demonstrate my inability to get much of anything
working with the MPL, I'm having trouble inserting a type into an existing
set of types.  The code compiles and runs, but the revised type sequence is
empty. 
Here's the code:

#include <boost/mpl/set.hpp>
#include <boost/mpl/for_each.hpp>
#include <typeinfo>
#include <iostream>

namespace mpl = boost::mpl;

struct Base { virtual ~Base(){} };
struct A { virtual ~A(){} };
struct B { virtual ~B(){} };

struct Print {
   template<typename T>
   void operator()(const T&)
   {
     std::cout << typeid(T).name() << ", ";
   }
};

int main()
{
   typedef mpl::set<A, B> Constraints;

   // print contents of Constraints (should be the equivalent
   // of "[A, B,]")
   std::cout << '[';
   mpl::for_each<Constraints>(Print());
   std::cout << "]\n";

   // add Base to Constraints, call result BaseClasses
   typedef mpl::insert<Constraints,
                       mpl::end<Constraints>,
                       Base> BaseClasses;

   // print contents of BaseClasses (should be the equivalent
   // of "[A, B, Base, ]")
   std::cout << '[';
   mpl::for_each<BaseClasses>(Print());
   std::cout << "]\n";
}

Can anybody spot what I'm doing wrong?  I know that I could use the
two-argument form of insert with a set, but I'm trying to write code that
will work with a vector, too, and at any rate, I get the same results with
the two-argument form of set.

Thanks,

Scott

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