How to utilize a class object in parameters of an overloaded operator?

[Tduck]

I've posted a sample of my code, in which I want to add the length of the rectangle passed in parameters to the current object's length, and width respectively. How would I do that though?

rectangleType rectangleType::operator+(const rectangleType& rectangle) const
{
    this->length += rectangle.length;
    this->width += rectangle.width;
}

[mbozzi]

Something like this:

rectangleType &rectangleType::operator+=(rectangleType const& rhs)
{
  this->length += rhs.length;
  this->width  += rhs.width;
  return *this;
}

// NOTE: non-member function
rectangleType operator+(rectangleType lhs, rectangleType const &rhs)
{
  return lhs += rhs;
}