I am having problems with creating a variable of pointer-to-member-function (PTMF) type "on the fly" (that is, by pinning some arguments of an existing member function via std::bind). My question is if it is ever possible with C++11 or post-C++11 standard.
Preambula: I have a class that stores a static const array of std::functions initialized from PTMFs, hereinafter referred to as "handlers". Originally, they were regular member functions with a name and implementation so I didn't ever use C++11 and std::function. Then, I decided that many of them are nearly similar, and decided to generate them with a "generator function". I would like to avoid using templates for the generation because the number of these nearly similar handlers is going to dramatically increase in future (around 200+) and templatizing will just lead to code bloat.
If the PTMFs in question were static, I would have no problems with generating the handlers via std::bind. A simplified example:
#include <iostream>
#include <functional>
using namespace std;
struct A {
typedef function<void(int)> HandlerFn;
static void parametrized_handler(int i, const char *param) {
cout << "parametrized handler: " << param << endl;
}
static void handler(int i) { cout << "handler 1" << endl; }
int mm;
};
static const A::HandlerFn handler2 = [](int) { cout << "handler 2" << endl; };
static const A::HandlerFn handler3 = bind(A::parametrized_handler,
placeholders::_1,
"test_param");
int main()
{
A::handler(42);
handler2(42);
handler3(42);
return 0;
}
Output:
$ ./a.out
handler 1
handler 2
parametrized handler: test_param
The problem arises when I turn to non-static member functions. std::bind is not able to generate a function object that acts like a PTMF. I know that I can pass a real object as a first argument to bind and get a working function but that is not what I want: when I am initializing a static const array, there are no objects at all, and the result of bind will act as a regular non-member function anyway.
An expected implementation for non-static member functions (with an imaginary std::bind_mem binder):
#include <iostream>
#include <functional>
using namespace std;
struct A;
struct A {
typedef function<void(int)> HandlerFn;
void parametrized_handler(int i, const char *param) {
mm;
cout << "parametrized handler: " << param << endl;
}
void handler(int i) const { mm; cout << "handler 1" << endl; }
const HandlerFn handler2 = [this](int i) { mm; cout << "handler 2" << endl; };
int mm;
};
// An imaginary PTMF binder
// static const A::HandlerFn handler3 = bind_mem(A::parametrized_handler,
// placeholders::_1,
// "test_param");
int main()
{
A a;
(a.handler)(42);
(a.handler2)(42);
//(a.handler3)(42);
return 0;
}
Output:
$ ./a.out
handler 1
handler 2
So is there a way to implement a PTMF argument binding?
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