Functionality of void operator()()

Question

I am confused about the functionality of void operator()().

Could you tell me about that, for instance:

class background_task
{
public:

            


        

Answer 1

The first part operator() is the way to declare the function that is called when an instance of the class is invoked as a function. The second pair of parentheses would contain the actual arguments.

With a return value and arguments this might make a bit more sense:

class Adder{
public:
int operator()(int a, int b){
    //operator() -- this is the "name" of the operator
    //         in this case, it takes two integer arguments.
    return a+b;
}
};
Adder a;
assert( 5==a(2,3) );

In this context, the std::thread will internally invoke f() inside the thread, i.e. whatever is inside the body of operator() is what gets done inside that thread.