rule of three - C++ : copy-and-swap idiom, alternative constructor -

nb: question follows a previous one, hope okay still ask new question.

i trying implement "three , half big rule" (copy-and-swap idiom) tree class, looks this:

class tree {     friend void swap(tree &first, tree &second); // swap function  public:     tree(const double &a, const double &b, int depth); // public constructor (derived default (private) constructor)     tree(const tree &other); // copy constructor     ~tree(); // destructor     tree & operator=(tree other); // copy-assignement operator   private:             tree(double *a, double *b, int depth, int maxdepth); // default (private) constructor      double *a, *b;     int depth, maxdepth;         tree *leftchild, *rightchild; }; 

i have been trying follow this guideline. here copy-assignment operator looks like:

tree & tree::operator=(tree other) {     swap(*this, other);     return *this; } 

i having hard time getting public constructor work. suggested like:

tree::tree(const double &a, const double &b, int depth) {     double atemp(a), btemp(b);     swap(*this, tree(&atemp, &btemp, depth, depth)); } 

i not sure idea works. in case following error compiler:

invalid initialization of non-const reference of type 'tree&' rvalue of type 'tree' in passing argument 2 of 'void swap(tree&, tree&)' 

i tried following idea instead, thought work:

tree::tree(const double &a, const double &b, int depth) {     double atemp(a), btemp(b);     *this = tree(&atemp, &btemp, depth, depth); } 

but not seem working either. think problem when call copy-assignment operator (*this = tree(&atemp, &btemp, depth, depth)), copy constructor should called (since argument of copy-assignement operator passed value), seems not happening. not understand why.

thanks in advance helping!

invalid initialization of non-const reference of type 'tree&' rvalue of type 'tree' in passing argument 2 of 'void swap(tree&, tree&)'

c++ not allow passing anonymous objects non-const reference. intent prevent callers accidentally throwing away results of functions write reference argument.

you instead do:

tree::tree(const double &a, const double &b, int depth) {     double atemp(a), btemp(b);     tree temp(&atemp, &btemp, depth, depth);     swap(*this, temp); } 

but not seem working either. think problem when call copy-assignment operator (*this = tree(&atemp, &btemp, depth, depth)), copy constructor should called (since argument of copy-assignement operator passed value), seems not happening. not understand why.

how determining it's not working? compiler might elide away copy avoid doing unnecessary work. (that why copy-assignment operator takes argument value.)

btw, if compiler supports c++11, use delegating constructors instead.