Operator Overloading question

[ILC]

Hi, I was reading a code, the purpose of it is creating a class which could create a dynamic array. There are some questions in its declaration. Hopefully, someone could help me.

The header file is as follow:

template <class T>
class Array
{ private:
T* alist;
int size;
void Error(ErrorType error,int badIndex=0) const;
public:
Array(int sz = 50);
Array(const Array<T>& A);
~Array(void);
Array<T>& operator= (const Array<T>& rhs);
Array<T> operator+ (const Array<T>& rhs);
T& operator[ ](int i);
operator T* (void) const;
int ListSize(void) const;
void Resize(int sz);
};


What I don't understand is that why the overloads of "=" and "[]" return references of T; however for the overload of "+", it returns an object of Array<T>.

Looking forward to some help, thank you very much.

[Disch]

= returns a reference to Array<T> to allow for "assignment chaining".

For example:

int a, b, c;

a = b = c = 5;  // legal

// the above is the same as
c = 5;
b = c;
a = b;

For this to work in overloaded = operators, the operator returns a reference to itself so that it can act as the rhs for another = operator.


The [] operator returns a reference to a T so that the retrieved element can be read/written to:

Array<int> myarray;

// myarray[5] returns a reference to element 5 of the array
//  references can be on the left or right side of an assignment:

int v = myarray[5];  // right side

myarray[5] = v; // left side.  Both legal if [] returns a reference. 

+ returns an object because it must create a new object. It cannot modify 'this'.

Example:

int a = 1;
int b = 2;
int c;

c = a + b;  // this does not modify a or b.
  // instead, a and b get added to a 'temporary' int, and that temporary int gets
  //  assigned to c