Question

Could someone explain this code? I don’t understand line 3:

MyString MyString::operator+(const MyString &str)
{
    MyString ss(*this); //----> explain this part
    ss += str;
    return ss;
}

Thanks!

Answer 1

This code:

MyString ss(*this);

Says “declare a new variable of type MyString that’s named ss, and initialize it as a copy of *this.” Inside of a member function, this is a pointer to the receiver object (the object that the member function is acting on), so *this is a reference to the receiver object. Consequently, you can read this as “make a new MyString that’s called ss and is a copy of the receiver object.”

The idiom being used here is implementing operator + in terms of operator +=. The idea is to make a copy of the receiver object, use operator += to add the parameter to the copy, and then to return the copy. It’s a widely-used trick that simplifies the implementation of freestanding operators given implementation of the corresponding compound assignment operator.

Hope this helps!