CODEWITHSUNDEEP
c++boostboost-bindboost-function
anorm
anorm

Reputation: 2263

boost::bind implicit conversion to boost::function or function pointer

I'm using boost::function like this:

template<class T1>
void run(boost::function<void (T1)> func, string arg)
{
    T1 p1 = parse<T1>(arg);
    func(p1);
}

When used like this, everything is ok:

void test1(int i)
{
    cout << "test1 i=" << i << endl;
}

...

boost::function<void (int)> f = &test1;
run(f, "42");

I want to be able to pass the raw function pointer directly, so I overload the run() function like this:

template<class T1>
void run(void (*func)(T1), string arg)
{
    T1 p1 = parse<T1>(arg);
    (*func)(p1);
}

...

run(&test1, "42"); // this is OK now

Now, I want to be able to pass the result of boost::bind to the run() function. Like this:

void test2(int i, string s)
{
    cout << "test2 i=" << i << " s=" << s << endl;
}

...

run(boost::bind(&test2, _1, "test"), "42"); // Edit: Added missing parameter 42

But this wont compile: Edited

bind.cpp: In function ‘int main()’:
bind.cpp:33:59: error: no matching function for call to ‘run(boost::_bi::bind_t<void, void (*)(int, std::basic_string<char>), boost::_bi::list2<boost::arg<1>, boost::_bi::value<std::basic_string<char> > > >, std::string)’
bind.cpp:33:59: note: candidates are:
bind.cpp:7:6: note: template<class T1> void run(boost::function<void(T1)>, std::string)
bind.cpp:14:6: note: template<class T1> void run(void (*)(T1), std::string)

How should I overload run() to accept boost::bind()?

Edit 2

I know I can do it like this:

boost::function<void (int)> f = boost::bind(&test2, _1, string("test"));
run(f, "42");

But I'd like the usage to be less verbose.

Edit 3

Changed run() prototype from run(boost::function<void (T1)>, T1) to run(boost::function<void (T1)>, string) to elaborate the actual use case. Ref. Igor R.'s answer

The entire source file may be obtained here

Upvotes: 0

Views: 1768

Answers (1)

Igor R.
Igor R.

Reputation: 15075

Neither function nor the result type of bind are convertible to a function pointer, so you can't pass them to run function with its current signature.

However, you can change run signature to allow it accepting any callable:

template<class F, class A1>
void run(F f, A1 arg)
{
  f(arg);
}

Now you can pass a pointer function, a binder, boost::function or what ever callable you wish - as long as it expects 1 argument. (Note however, that with this trivial signature run wouldn't forward the arguments to f seamlessly.)

Upvotes: 1

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