Re: [Boost-users] Inconsistency between boost::bind andboost::lambda::bind

Gerardo Lamastra wrote:

So, my first question would be: where could I find an exhaustive comparison between these two facilities? And, is there any indication on what to prefer, also related to future development and/or inclusion in C++ standards (If I remember well, boost::lambda has been proposed in tr1?)

Nobody has written an exhaustive comparison between boost::bind and lambda::bind, but the general rule is to use lambda::bind if you use Lambda, boost::bind otherwise. :-) TR1 contains a 'bind' that is a superset of boost::bind. Both boost::bind and boost::lambda::bind are reasonable approximations of std::tr1::bind.

The situation is the following: if I try to create a nullary lamnda function with boost::lambda::bind() like this:

generate_n(inserter(v, v.begin()), 10, boost::lambda::bind( boost::lambda::new_ptr<Slave>(),*this) );

the compiler fails to compile: it tries to pass the this pointer as a const reference somehow, and then it fails claiming that a Slave(const Master& m) cannot be found; If I try to add one, it fails with a similar error.

If I substitute the boost::lambda::bind() with a boost::bind(), it compiles & works perfectly.

Your code seems wrong. Remember that bind makes a copy of its arguments, '*this' in this case. So when you construct a new Slave, its reference is initialized to this internal copy of *this. The function object then disappears and the result is a dangling reference. Use boost::ref(*this). Now, if you are interested in why Lambda doesn't accept the code whereas Bind does: Lambda always makes these internal copies const. boost::bind propagates the const-ness of the function object to its members. In this case the function object is non-const and so is the internal copy of *this.