Hah, what a coincidence. I see that Hajo Kirchhoff has just asked basically the same question two hours before me. See "[Boost-users] [function] function_equal or function::operator== ambiguous overload?" Is this something which has changed in 1.36.0? Will go check with an older version... Best regards, Christian Christian Larsen skrev:

Hi,

I'm storing function objects in a std::vector, but to remove one again, I need to find an iterator to the one I want to remove. I do this in an "unregister" function taking a single boost::function<void ()> as parameter. Inside the function I would like to use the std::find algorithm to get an iterator to that function in the vector. I'm getting compile errors, though; see the example below. How do I fix these?

I'm using MSVC++ 8 (SP1), and Boost 1.33.1 (can not upgrade).

Example, where in my "unregister" function I use find as in the last part of this example (i.e. I have a Listener and not a plain function pointer). This does not compile:

#include <algorithm> #include <vector> #include <boost/function.hpp>

using namespace std; using namespace boost;

void listenerA() {} void listenerB() {}

int main() { typedef function<void ()> Listener; typedef vector<Listener> ListenerVector;

ListenerVector listeners;

listeners.push_back(&listenerA); listeners.push_back(&listenerB);

ListenerVector::iterator iter;

// This compiles and works iter = find( listeners.begin(), listeners.end(), &listenerB);

assert(iter != listeners.end());

// This gives: // error C2666: 'boost::operator ==' : 4 overloads have // similar conversions iter = find( listeners.begin(), listeners.end(), Listener(&listenerB));

assert(iter != listeners.end());

return 0; } [SNIP]

Christian Larsen skrev:

I'm storing function objects in a std::vector, but to remove one again, I need to find an iterator to the one I want to remove. I do this in an "unregister" function taking a single boost::function<void ()> as parameter. Inside the function I would like to use the std::find algorithm to get an iterator to that function in the vector. I'm getting compile errors, though; see the example below. How do I fix these?

Sorry for spamming the list. I think I found a solution to my original problem. But still I'm not completely satisfied, because it seems there is no way I can store the function objects and use those for both adding and later removing. If I try to store them using boost::function I get the same error as before when calling either Source::add or Source::remove, obviously because std::find tries to compare two boost::function's internally. This example does what I expect, but would it somehow be possible to store the bind(&listenerA, 42) for later use in the remove call? (Having to write the same in both places is error prone.) #include <algorithm> #include <iostream> #include <vector> #include <boost/function.hpp> #include <boost/bind.hpp> using namespace std; using namespace boost; typedef function<void ()> Listener; typedef vector<Listener> ListenerVector; struct Source { ListenerVector listeners; template <typename F> void add(F f) { ListenerVector::iterator iter = find( listeners.begin(), listeners.end(), f); assert(iter == listeners.end() && "already added"); listeners.push_back(f); } template <typename F> void remove(F f) { ListenerVector::iterator iter = find( listeners.begin(), listeners.end(), f); assert(iter != listeners.end() && "not added"); listeners.erase(iter); } void signal() { for (ListenerVector::iterator iter = listeners.begin(); iter != listeners.end(); ++iter) { (*iter)(); } } }; void listenerA(int) { cout << "Hello, "; } void listenerB(float) { cout << "World!\n"; } int main() { Source s; s.add(bind(&listenerA, 42)); s.add(bind(&listenerB, 3.14f)); s.signal(); // "Hello, World!" s.remove(bind(&listenerA, 42)); s.signal(); // "World!" s.remove(bind(&listenerB, 3.14f)); s.signal(); // <nothing> return 0; } Best regards, Christian