Question

I have a map of std::unique_ptr of type foo, and I’m trying to iterate the map, passing the value of each to a public member of a foo not in the map. I’m close, but I can’t figure out how turn the result of the inner most bind from a reference to a pointer.

Given:

class foo
{
public:
    bool DoWork(foo *);
};

std::map<long, std::unique_ptr<foo> map_t;

map_t foo_map_;
foo bar_;

std::for_each(std::begin(foo_map_), std::end(foo_map_), std::bind(&Foo::DoWork, &bar_, std::bind(&std::unique_ptr<foo>::get, /* This guy here -->*/std::bind(&std::pair<long, std::unique_ptr<foo>>::second, std::placeholders::_1))));

Recommendations? I’m using Visual Studio 2010 SP1.

Answer 1

The compiler error is due to the fact that std::map const’ifies the key type, so that the value_type of map_t is not std::pair<long, std::unique_ptr<foo> > but rather std::pair<long const, std::unique_ptr<foo> >. To avoid such errors prefer using map_t::value_type. The following change fixes the error:

... std::bind(&map_t::value_type::second, std::placeholders::_1) ...

In C++11 you can simplify it to:

for(auto const& kv : foo_map_)
    bar_.DoWork(&*kv.second);

Or, using std::for_each and C++11 lambda:

for_each(foo_map_.begin(), foo_map_.end(), 
    [&bar_](map_t::value_type const& kv) { bar_.DoWork(&*kv.second); });