How to Store Member Function Pointers in Generic `std::function` Objects?

Storing Member Function Pointers in Generic std::function Objects

When attempting to store member function pointers of a particular class in a map using std::function objects, developers may encounter an error: "term does not evaluate to a function taking 0 arguments." This error arises when assigning the member function pointer directly to the std::function object.

The crux of the issue lies in the fact that non-static member functions require an implicit "this" pointer as the first argument. To rectify this, the first argument must be explicitly bound.

Solution:

std::function<void(void)> f = std::bind(&Foo::doSomething, this);

This approach effectively binds the "this" pointer as the first argument, allowing the std::function object to correctly capture the member function.

Handling Functions with Parameters:

For member functions with parameters, placeholders must be specified to indicate the position of the bound arguments.

using namespace std::placeholders;
std::function<void(int, int)> f = std::bind(&Foo::doSomethingArgs,
                                                 this,
                                                 std::placeholders::_1,
                                                 std::placeholders::_2);

C 11 Lambda Syntax:

If the compiler supports C 11 lambdas, a more concise approach can be utilized:

std::function<void(int, int)> f = [=](int a, int b) {
    this->doSomethingArgs(a, b);
};

By following these techniques, developers can effectively store and invoke member function pointers using generic std::function objects.

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