Regarding your EDIT: that is not a valid way of modifying x. When you try to assign a new foo that way, what you are implicitly doing is calling the copy assign

Regarding your EDIT: that is not a valid way of modifying x. When you try to assign a new foo that way, what you are implicitly doing is calling the copy assignment operator. This normally works by copying each field from the input object to the destination object, but, since the field x is const, it cannot be re-assigned to the input object's x. In fact, very often the compiler will generate a copy assignment operator implicitly for you, but not in this case, because it can't copy values into a constant field. Also, since you have a local pointer f within some_func, so re-assigning a new object of type foo to it will not alter the original foo. This is not implied by your original comment but it's something one could wonder.