boost :: bind绑定到类成员函数

Question

I'm trying to pass member function wrapped to stand-alone function via boost::bind . The following is the reduced sample.

// Foo.h
typedef const std::pair<double, double> (*DoubleGetter)(const std::string &);

class Foo : private boost::noncopyable {
public:
  explicit Foo(const std::string &s, DoubleGetter dg);
};

// Bar.h
struct Bar {
  const std::pair<double, double> getDoubles(const std::string &s);
};

// main.cpp
boost::shared_ptr<Bar> bar(new Bar());

std::string s = "test";
Foo foo(s, boost::bind(&Bar::getDoubles, *(bar.get()), _1));

However I got compiler error with the text:

/home/Loom/src/main.cpp:130: error: no matching function for call to 
‘Foo::Foo
( std::basic_string<char, std::char_traits<char>, std::allocator<char> >
, boost::_bi::bind_t
  < const std::pair<double, double>
  , boost::_mfi::mf1
    < const std::pair<double, double>
    , Bar
    , const std::string&
    >
  , boost::_bi::list2
    < boost::_bi::value<Bar>
    , boost::arg<1>
    >
  >
)’

/home/Loom/src/Foo.h:32: note: candidates are: 
Foo::Foo(const std::string&, const std::pair<double, double> (*)(const std::string&))

/home/Loom/src/Foo.h:26: note:
Foo::Foo(const Foo&)

What the problem with the code and how to avoid such a problems?

Answer 1

Member function pointers do not include a context (as opposed to a lambda or boost::function ). To make the code work you need to replace your type definition of DoubleGetter to:

typedef boost::function<const std::pair<double, double>(const std::string&)> DoubleGetter;

Also there is also no need to dereference the smart pointer when you supply the context ( Bar )(if you intend to do so anyway you can use the shorthand dereference operator directly):

// Pass the pointer directly to increment the reference count (thanks Aleksander)
Foo foo(s, boost::bind(&Bar::getDoubles, bar, _1));

I also noticed that you define a normal function pointer. In case you want to avoid use of boost::function completely you can use the following approach (I excluded non-altered parts):

typedef const std::pair<double, double> (Bar::*DoubleGetter)(const std::string &);

class Foo : private boost::noncopyable {
public:
  explicit Foo(const std::string &s, Bar& bar, DoubleGetter dg);
  // Call dg by using: (bar.*dg)(s);
};

// Instantiate Foo with:
Foo foo(s, *bar, &Bar::getDoubles);