What does “int& foo()” mean in C++?

Question

While reading this explanation on lvalues and rvalues, these lines of code stuck out to me:

int& foo();
foo() = 42; // OK, foo() is an lvalue

Answer 1

The function you have, foo(), is a function that returns a reference to an integer.

So let's say originally foo returned 5, and later on, in your main function, you say foo() = 10;, then prints out foo, it will print 10 instead of 5.

I hope that makes sense :)

I'm new to programming as well. It's interesting to see questions like this that makes you think! :)