mem_fun and bind1st problem

Question

I've following class:

class A {
public:
// ctr and etc ...
A*   clone(B* container);
};

Now, I've a vector<A*> availableObjs populated already. I want to call clone on each of those, so and insert cloned objects into a new container clonedObjs of type vector<A*>. I'm trying following - but it doesn't compile:

transform(availableObjs.begin(), availableObjs.end(), back_inserter(clonedObjs),
    bind1st(mem_fun(&A::clone), container)); // container is of type B*

Is there a easy way out? I've a lot classed like A - so making each of those a functor is too much task.

Suprasegmental

Are you sure you want to have pointers in your container? You must not call any modifying algorithm on that algorithm (like for example sort). However, you could use a vector of shared_ptr<A*>, then you support value semantics again. – Castiglione

Answer 1

You need to use bind2nd instead of bind1st:

transform(availableObjs.begin(), availableObjs.end(), back_inserter(clonedObjs),
    bind2nd(mem_fun(&A::clone), container)); // container is of type B*

The functor created by mem_fun(&A::clone) expects an A* as its first parameter. This is the normally implicitly specified instance on which the method is called. The first "real" parameter of A::clone is the second parameter of mem_fun(&A::clone) and therefore needs to be bound with bind2nd.

Pillage

Answer 2

If you use Boost.Bind it might look like this:

std::transform(
               availableObjs.begin(), availableObjs.end(), 
               back_inserter(clonedObjs),
               boost::bind<A*>(boost::mem_fn(&A::clone), _1, container) ); 

Meng