std::function

Brief

std::function is a simple yet powerful type. It can basically store any function: this allows you to pass functions as parameters to other functions, or to store a function for later use.

#include <functional>

std::vector<std::function<void()>> callbacks; // A list of functions that we will call when some special event happens.

A std::function can be a lambda:

callbacks.push_back(
    []() { std::cout << "Lambda\n"; }
);

or a function pointer:

void my_callback() {
    std::cout << "Function pointer\n";
}

callbacks.push_back(
    &my_callback
);

or a function object:

struct MyCallback {
    void operator()() const {
        std::cout << "Function object\n";
    }
};

callbacks.push_back(
    MyCallback{}
);

We would than use our callbacks like so:

for (const auto& callback : callbacks) {
    callback();
}

Signature

std::function stores functions with a given signature. For example std::function<int(float)> is a function that takes a float and returns an int.