Question

I was wondering if (in C++) you can instantiate a class (class foo) then have said class return the already instantiated object. (foo::instance())

In other words, can I have a class return it’s-self via it’s own methods? I want to be able to create a class (i.e. class foo) early in my program so it is already setup and ready to go. Then, farther down the line, I want to be able to call functions from that class without having to pass that object as an argument to my calling function. Can I do something like so:
MyClass::ReturnSelf()->foo();
or
MyClass::ReturnSelf().foo();

EDIT: I just realized this might be a little unclear. I want to be able to have another class call this “self-returning” method so it can use the already instantiated object’s methods and members without creating a new object.

Answer 1

Congrats, you’ve discovered the singleton pattern. Quite a caveat, if you didn’t already know it.

struct X
{
   static X& instance()
   {
       static X x;
       return x;
   }

   void foo();
};

and call the method as:

X::instance().foo();

Of course, you could also make the method static, if that’s an option, and call it directly:

X::foo(); //this requires foo to be declared static

The effect of returning the instance from methods can also be used for method chaining:

struct Element
{
    Element& setColor() { return *this; }
    Element& setWidth() { return *this; }
};

Element e;
e.setColor().setWidth();