What are some examples of function objects in C++?

What are some examples of function objects in C++?

Function objects, or functors, are objects that can be called as if they were functions. For example, you can define a class with an overloaded operator() to create a function object.

Can you show me a simple example of a function object?

Sure! Here's a simple example:

class Adder {
public:
    Adder(int x) : x_(x) {}
    int operator()(int y) const { return x_ + y; }
private:
    int x_;
};

int main() {
    Adder add5(5);
    std::cout << add5(3); // Outputs 8
}

This creates a function object that adds a fixed value to its input.

What are the advantages of using function objects?

Function objects can maintain state, can be passed around like regular functions, and can be more efficient than using function pointers.

Are there any standard library function objects I can use?

Yes! The C++ Standard Library provides several function objects like std::plus, std::minus, std::multiplies, and more, which can be used with algorithms.