Returning Objects by Value

Returning Objects by Value

For efficiency reasons, large objects should usually be passed to or returned from a function by reference or by their address (using a pointer). There are, however, a few circumstances in which the best choice is to return an object by value. A good example is an overloaded operator +. It has to return a result-object, yet it may not modify any of its operands. The seemingly natural choice is to allocate the result-object on the heap (using operator new) and return its address. But this is not such a good idea – dynamic memory allocation is significantly slower than local storage. Also it may fail and throw an exception which has to be caught and handled; worse it can lead to memory leaks since it is unclear who’s responsible for deleting this object – the creator or the user? Another solution is to use a static object and return it by reference. This is also problematic, since on each invocation of the overloaded operator, the same instance of the static object is being modified and returned to the caller, resulting in aliasing. Consequently, the safest, less error prone and most efficient solution is to return the result-object by value:

 class Date {	int d,m,y;public:	Date operator + (const Date& other) const { Date temp = *this; temp += other; return temp;} };


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