Re: Using boost::lambda with std::count_if

I have following class:

class User
{
public:
     enum Status
     {
         Online,
         Away
         Offline
     };

     User(const std::string & name, Status status);

     Status status() const;

     const std::string & name() const;

private:
     std::string mName;
     Status mStatus;
};

And I have a vector:
std::vector<User> users;

Now I want to use count_if to count all users that have not the
Offline status. I can do this by writing a predicate function of
course but I think it would be nice to do this using a lambda
expression.

I can't figure out how to write the expression. Idealy it would look
something like this I think:
count_if(users.begin(), users.end(), lambda::_1.status() !=
User::Offline);
But that doesn't compile, as I expected.

Another question: suppose I do write following predicate functions:

bool Predicate_UserOnline(const User& user)
{ return user.status() == User::Online; }

bool Predicate_UserAway(const User& user)
{ return user.status() == User::Away;}

bool Predicate_UserOffline(const User& user)
{ return user.status() == User::Offline; }

Is it then possible to count the users, using count_if, that are
either Online or Away? It would be !Predicate_UserOffline, but I can't
use that expression as a function pointer.