c++ template instantiation duty template parameters

i have following problem controlling template instantiation [*].

file foo.h

class foo
{
public:
    template <typename f>
    vacant func(f f)

private:
    int member_;
};

file foo.cc

template <typename f>
foo::func(f f)
{
     f(member_);
}

file caller.cc

foo::func(boost::bind(&bar::bar_func, bar_instance, _1));

while compiles fine, linker complains an capricious symbol:

void foo::func<boost::_bi::bind_t...>

how i instantiate function foo::func? given takes duty argument, i am small bit confused. i attempted supplement an instantiation duty foo.cc, i am used unchanging non-function types:

instantiate()
{
    template<> vacant foo::func<boost::function<void(int)> >(boost::function<void(int)>);
}

obviously, does work. i conclude someone indicate me right direction.

thanks!

[*] yes, i review parashift faq lite.