Why do I need to delete resources when using copy-assign operator?

Question

Code like this from one of my books for example:

class HasPtr {
public:
    HasPtr(const HasPtr& h): ps(new std::string(*h.ps)), i(h.i) { }
    HasPtr(const std::string &s = std::string()): ps(new std::string(s)), i(0) { }
    HasPtr& operator=(const HasPtr&);
    ~HasPtr() { delete ps; }
private:
    std::string *ps;
    int i;
};

HasPtr& HasPtr::operator=(const HasPtr &rhs){
    auto newp = new string(*rhs.ps); // copy the underlying string
    delete ps; // free the old memory
    ps = newp; // copy data from rhs into this object
    i = rhs.i;
    return *this; // return this object
}

Seems like the inside of the operator= could just be:

*ps = *rhs.ps
i = rhs.i
return *this;

With no need to delete the pointer first, seems redundant to do so. It did mention it is written in a way to leave the object in a suitable state should an exception occur but didn't divulge past that, but I don't see what exception could occur that even my alternative wouldn't handle. Why is there a need to delete the object first before assigning?

Answer 1

In this case, yes, that would be fine.

You're not leaking the dynamically-allocated string: you're re-using it.